Meridian America DJ Equipment Meridian 518 User Manual

MERIDIAN 518 USER MANUAL

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Simple rules for using 518..................40

Additional technical information.........42

Specification.........................................42

Help!......................................................43

Appendix 2 – Hints on Mastering

with noise-shaping ......................... 47

Appendix 3 – RS232............................. 49

Appendix 4 –Resolution

Enhancement .................................. 50

Standby point not lit ...........................43

Audible hiss at high volume

settings.........................................43

No output with Meridian 565,

DSP speaker or DAC....................43

No time display with Meridian

DSP speaker ................................43

Communications not working

Jitter and de-jittering.......................... 50

Dynamic-range.................................. 51

Dynamic-range optimisation

with Gain...................................... 52

Dynamic-range optimisation

with Pre-emphasis........................ 52

Dynamic-range optimisation

with Noise-shaped Dither ............. 54

DAC enhancement by using

between 518 and other

Meridian products. ........................43

Radio interference .............................43

high-frequency dither.................... 55

DAC or channel enhancement

Cleaning................................................44

Maintenance & Service.........................44

Part 3.....................................................45

Appendix 1 – Noise Shapes.................45

by word-length matching .............. 55

Index..................................................... 56

Notes..................................................... 58

518 User Guide

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Sales and service in the UK

Meridian Audio Ltd

Stonehill

Huntingdon

Cambs. PE18 6ED

England

Tel (0) 480 52144

Fax (0) 480 459934

Sales and service in the USA

Meridian America Inc.

3800 Camp Creek Parkway

Building 2400, Suite 112

Atlanta, GA 30331

Tel. (404) 344-7111

Fax (404) 346-7111

Designed & manufactured in the UK by

Digital Gramophone & Wireless Ltd

Stonehill

Huntingdon

Cambs. PE18 6ED

England

Acknowledgements

Trademarks etc.

Boothroyd|Stuart Meridian and Meridian are registered trademarks of

Meridian Audio Ltd.

Super Bit-Mapping is a trademark of Sony Corp.

Testers

The processing in 518 has been beta tested in a 618 version over some

three years. Thanks in particular to Tony Faulkner (Green Room

Productions), David Chesky (Chesky Records), Tom Jung (DMP

Recording), David Smith (Sony Classical), Peter McGrath (Audiophon,

HM) and John Atkinson (Stereophile Magazine).

A list of their current 618 recordings is available from Meridian Audio on

request.

Designers

The 518 design team included Phil Boddy, Richard Hollinshead, Duncan

Smith, Bob Stuart and Rhonda Wilson.

Author: J R Stuart

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Installation

Introduction

The Meridian 518 Digital Audio Processor is part of the 500 Series of

advanced high-fidelity equipment.

In purchasing a Meridian 518 Digital Audio Processor, you have acquired

a refined piece of equipment that will continue to bring you listening

pleasure for many years. This manual will enable you to get the most from

it.

About this manual

Because the 518 is such a flexible item, we have divided this manual into

three parts.

Part 1 gives an overview of 518 and gives 'how to use' information for the

two common 'consumer' applications of Control Unit and Resolution

Enhancement.

Part 2 is more technical and describes how to use 518 as a Mastering or

Multimedia Processor.

Part 3 gives more technical information in Appendices.

Conventions used in this manual

506. A number such as 506 refers to a component in the Meridian 500

Series of audio equipment.

Display. Whenever a key name is printed in bold typeface, it means that

you should press this key. If the key name is not in bold type, it

indicates that the course of action is not required at present, e.g. ‘if

you want to change the display, press Display' means you can do this,

but it is not essential as part of the operation currently being

discussed.

Standby Italic form normally refers to the state of the 518. In some in-

stances, a key and the status of the equipment share the same name,

e.g. the Standby key and the Standby state.

Radio

Displays are illustrated in this form.

1. Sequences of actions are given in numbered lists.

About the 500 Series

The Meridian 500 Series is a unique system of digital, analogue and video

components designed to meet the demand for absolute quality, ease of

use and lasting value.

The flexibility of the Meridian 500 Series is such that you can assemble a

system as simple or as complex as you need, perfectly suited to your

requirements, and with the ability to add to it or change it at a later date

should those requirements change.

The Meridian 500 Series includes a sophisticated communications link, to

ensure that any configuration of units will work together as a fully

integrated system. The 500 Series communications system allows you to

control any combination of units using a single handset, and ensures that

your commands from the handset are interpreted unambiguously. Any

unit can be designated as the controller for the system, allowing you to

position the other units out of range from the handset beam if desired. It

also allows all the units to be switched off from the front panel of any unit

in the system.

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Installation

Part 1

Unpacking the 518

On opening the carton, you should have found the following parts:

Meridian 518 Digital Audio Processor

Power cord

This manual

500 Series communications lead

If any of these items is missing, please contact your dealer. We suggest

that you retain the packing carefully as it provides maximum protection for

the unit in transit.

Installing your 518

General precautions

Before carrying out any installation, you should ensure that the 518 is

marked with the correct voltage for your local AC supply. Should this not

be the case, do not proceed – but contact your dealer.

As a general rule, you should not make any connections to the 518, or to

any other component in your system, whilst the AC power supply is con-

nected and switched on.

Connections

There are three types of connection that need to be made to the 518:

power

digital audio

communications.

Audio connections need to be made to other components in your system.

Communication connections have to be made to most of the other

Meridian components in your system in order for them to act as one sys-

tem. The connections to your 518 are very important and care should be

taken in deciding which connections to make.

Connection details are described following page 29.

Siting

We recommend the following guidelines for location.

The 518 should not be placed on top of a power amplifier.

Avoid sites where it would be subjected to direct sunlight or where it is

near a heat source, e.g. a central heating radiator

Avoid sites where the 518 could be subjected to strong magnetic ra-

diation, like near a power amplifier.

Not too close to a television, or where connecting cables may be sub-

ject to, or cause, interference.

Tip In common with all digital products, the 518 emits some radio-fre-

quency signals. For this reason, try to keep all power cables and network

leads away from audio, antenna and loudspeaker cables. Some time

spent laying out the cables carefully will repay you with the best possible

performance later.

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Overview of 518

Planning setup of 518

Firstly, the 518 is a product for enthusiasts! We designed it for audio and

multimedia enthusiasts, keen listeners and those with enthusiasm for the

best sound.

However, 518 is something of a chameleon. What do we mean by that?

This is best explained by seeing what it does: 518 fulfils four very different

functions in one box.

We have categorised uses (applications) of 518 into four broad headings,

as follows:

A simple 'preamp' or Control Unit for a purist digital audio system.

(Type 0) – see below.

A Resolution Enhancement processor in a high-quality audio system.

(Type 1) – see the overviews on pages 10 and 49.

A Mastering Processor, used in any recording, editing, mastering or

dubbing process. (Type 2) – see the overview on page 12.

A peri-computer Multimedia Processor. (Type 2) – see the overview

on page 12.

What's inside a 518?

Input Switch

Twin PLL

42MHz DSP

Digital Output

Out

Opt

Control

Computer

Front Panel

RS232

Internal block diagram for 518

518 is a 2-channel digital audio computer with four inputs – see the

diagram above. The selected input is de-jittered with a proprietary

Meridian twin phase-lock-loop that acts as a 'big flywheel' to regulate the

audio stream. By using this twin PLL we ensure that the outgoing digital

audio has very precise timing allowing the final output device (e.g. DAC)

to achieve its maximum sonic potential.¹

Following the twin PLL is a fast (42MHz) 24-bit Digital Signal Processor,

which runs the user programs in 518. The DSP functions are all controlled

by an internal computer which co-ordinates the front-panel keys, remote

control sensor and display as well as RS232 control.

All software for 518 – control and DSP is held in a socketed EPROM. This

allows the potential of upgrades or new applications being issued later.

Following the DSP is a multistandard digital output.

¹For the technically interested, Figure 1 on page 49 shows the

performance of the twin PLL.

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Overview of 518

Overview as Preamp (Type 0)

Conventional analogue systems use a 'preamp' or control unit to gather

together the various sources and to control the level of signal fed to the

power amplifier so you can adjust volume.

Purists know that no matter how well a piece of analogue audio

electronics is designed, there will always be unwanted and irreversible

degradation, due to the addition of noise and distortion. Preamps are by

no means immune from this.

For this reason, Meridian have for many years been developing an all-

digital system where digital audio is handled by a digital controller (like

562) instead of a preamp. In these systems the signal is kept in the digital

domain right into the DSP loudspeakers. Apart from sophisticated

loudspeaker technology, the digital signal processing (DSP) in the

speakers also replaces the volume control.

Some quality-concious audiophiles (who still don't have DSP speakers)

prefer to use very simple replacements for the analogue preamp, placing

a passive volume control between an analogue source such as a CD

player or DAC and the power amp. This architecture gives very high

sound quality, but has a number of disadvantages – like it requires a very

sensitive power amp and has difficulties with impedance matching, hum,

noise and frequency response in the passive control.

The Meridian 518 can provide an enormous improvement in the sound

quality of some systems, by allowing you to dispense with the analogue

preamp altogether – providing you have a good enough digital–analogue

converter (DAC) and can route all signals in digital form.

For these applications – where a DAC can be connected directly to a

power amp – then 518 provides a radical upgrade by removing the

troublesome passive control.

CD Player

518

DAC

Power Amp

LaserDisc

DAT

Using 518 as a 'preamp'

The system is illustrated above. Up to four digital sources – like CD, DAT

or LaserDisc (often using the optical input) – are connected to the 518.

518 is then configured as Type 0 (see page 21) which makes it a system

controller with a fully-operational volume control.

The output of 518 is taken to a DAC (or digital power amp); the output of

the DAC is directly connected to the power amplifier.

The 518 performs more functions than switching and volume control. In

summary, it:

smooths the sound by de-jittering the incoming data stream,

performs resolution enhancement by word-length matching, shaped

dither DAC enhancement and the option of pre-emphasising the DAC.

For an overview of Resolution Enhancement see page 49.

Warning! Systems like this can sound incredibly good!

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Overview of 518

What about analogue sources?

Tuner

562

518

CD Player

LaserDisc

DAT

Using 518 with a 562

Analogue sources need to be converted to digital before passing through

518. Meridian make the 562 and 562V digital controllers, both of which

have very high quality delta-sigma analogue–digital converters.

By adding a 562 to the system you will be able to feed 7 analogue

sources (like radio, tape, even LP) in addition to 5 digital sources. A 562

also provides full tape copy and 2-room facilities.

518 and 562 work together seamlessly through the Meridian 500 Comms

system.²

What else do I need to know?

This is a high-performance system, and to be successful, there are a few

things to consider.

Use a high-quality DAC. Preferably look for at least 18 bit precision.

The Meridian 563 is an 18 bit converter and is a very good choice. Of

course, 16 bit DACs will work, and the sound quality improvements

from 518 will be evident: the drawback is that 16 bit DACs may give

an audible background hiss when connected directly to a power

amplifier. The extent of this noise depends on the sensitivity of the

power amplifier and speaker used – and of course will be no more

than the noise the DAC currently gives you at high listening levels.

If the power amp has some adjustment, set its gain to the lowest

value that also allows 518 to give you the loudest result you need. As

a guideline, an 18 bit DAC should be quiet enough for a system where

the DAC maximum output (normally 2V) is well matched to the power

amp sensitivity.

Make sure that the maximum output of the DAC (normally around 2V)

suits the maximum input level of the power amp. Your dealer will

advise on this.

As there is no volume control between the DAC and power amp, it is

important that either the DAC you use does not have a serious turn-

on/off thump, or that you always turn the power amp on last and off

first.

Preferably, the DAC will use analogue de-emphasis.

²Setup details: set 518 to Type 0, set 562 to Type 1. Either can be the

system controller. Autoconfigure (see page 30) makes 562 the controller.

Make 518 the controller if you want to use the Menu keys on MSR.

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Overview of 518

Overview as Resolution Enhancement Processor

(Type 1)

There are a wide number of applications for this mode of 518: three

examples are described.

CD or LaserDisc playback improvement

Many installations use the 2-box CD player format of CD transport + DAC.

The CD transport provides a digital output, and of course may be a

normal CD player where the digital output is used to drive an outboard

DAC to improve the quality.

This CD playback system may then have its analogue output connected

to a preamp or integrated amplifier in the usual way.

Analogue inputs

CD Player

518

DAC

Preamp

LaserDisc

Using 518 as part of CD playback

The diagram above illustrates how 518 is added to such a system. The

picture shows that the source could be a CD transport, a LaserDisc player

or both.³

The 518 provides two resolution enhancement methods: de-jittering via

the twin PLL and DAC optimisation through DSP. These are explained in

'Overview of Resolution Enhancement' – page 49.

The de-jittering element is of great importance to some CD players, and of

enormous significance to any LaserDisc player as they tend to have

relatively high-jitter output. If you want to use a LaserDisc player for

serious CD listening, then the de-jittering in 518 is absolutely necessary.

The DSP DAC optimisation uses the techniques described in Appendix 4.

One function the 518 provides is matching the wordlength of the source to

the capability of the DAC, so for example, it can match LaserDisc or CD

(both 16 bits) to an 18 or 20 bit DAC.

Normally in this mode, the 518 is not used as a volume control. Optimum

performance for a disc will come, either from using unity-gain (i.e. 0dB

gain) or possibly a few dB boost to optimise the disc.

Meridian DSP speaker improvement

The Meridian DSP loudspeakers, provide the most advanced performance

and highest-resolution sound available today. The DSP speakers only

accept a digital input and in order to use analogue sources a Meridian 562

or 562V is often added. The 562 provides input handling for up to seven

analogue signals using its in-built 16 bit delta-sigma analogue-to-digital

converter (ADC).

³Setup details: set 518 to Type 1. Adjust Out to match DAC.

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Overview of 518

DSP

Speaker

Tuner

562

518

CD Player

LaserDisc

DAT

DSP

Speaker

Using 518 with DSP Loudspeakers

As the diagram shows, a 518 can be placed between the 562 and the

Meridian DSP speakers. In this case, the 518 is used – very much as it is

for the earlier CD example – to provide further de-jittering and resolution

enhancement. The Meridian DSP speakers can read 22 bits on the input

and have analogue de-emphasis, so 518 can significantly improve the

sound of this system.⁴

Because 518 does not pass on subcode, the time display feature on

DSP5000 or DSP6000 becomes disabled. However the Meridian Comms

system keeps the speaker updated on the current track number.

Meridian Surround improvement

The Meridian 565 is a world-beating surround decoder. One of its unusual

features is the ability to accept digital signals directly to the DSP

decoding. This means, for example, that the signal from a LaserDisc can

be passed without the distortion of in-built (and often inferior) DACs and

results in a substantially improved sound.

The Meridian 565 can drive DSP, active or conventional loudspeakers in

any combination.

Tuner

562V

518

565

CD Player

LaserDisc

DAT

Using 518 with a 565 Digital Surround Processor

Whatever the output configuration, the 518 should be placed before the

565 Digital Surround Processor – so that the precision of the inputs

(normally 16 bit) can be matched to the 20 bit input capability of 565.⁵

⁴Setup details: set 518 to Type 1. Set Out to 22 C.

⁵Setup details: set 518 to Type 1. Set Out to 20 C.

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Overview of 518

Overview as Mastering Processor (Type 2)

Recorder

Mixer

ADC

DAT

518

Recorder

Using 518 as a Mastering Processor

The 518 is closely related to the highly respected Meridian 618 Mastering

Processor; in fact 518 uses identical DSP to the 618 in this mode.

The Meridian 618 has been used for over three years by some of the

world's most experienced recording engineers and there is a long and

growing list of superior CDs that have used 618 in their production. See

page 4.

A mastering processor is used during recording, editing and transfer

processes. In the course of making a CD for example, the music may

pass through 518 two, three or four times.

The diagram shows 518 between a recorder – which may be DAT, reel–

reel, CDR, MO or hard disk – and a source which may be also a recorder

or an analogue-to-digital converter (ADC).

The Mastering processor provides these important functions at each

stage:

de-jittering

matching wordlengths output to input

translating between consumer and professional serial interface modes

stripping subcode and some flags

level-shifting to optimise dynamic range

fading during edits

multiple re-dithering options

DSP application of pre-emphasis or de-emphasis

RS232 control

Overview as Multimedia Processor (Type 2)

CDR

Computer

ADC

DAT

Mixer

518

Computer

Speaker

CD/DAT

Using 518 as a Multimedia Processor

The Multimedia application of 518 is somewhat similar to the Mastering

Processor just described.

Inevitably a PC is a very unfriendly place for high-quality sound for a

number of reasons. The nature of the electrical environment, the block

(i.e. 'jerky') access of hard-disc data and severe electrical noise combine

to seriously limit the jitter performance of digital audio functions and the

analogue performance of sound cards.

The principle benefits of using 518 in multimedia systems are:

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Overview of 518

De-jittering. This is vital to getting good sound when recording or

playing back from a computer-based sound storage system.

Matching wordlengths input to output. Hard disc storage systems tend

to use 16 or 24 bits. While 16 bit storage is quite adequate for simple

transfer, it does not allow any headroom for manipulation of the

signals – without degrading noise. 518 can be used to ensure that all

the headroom in the disc storage is used by boosting the incoming

signals to full code. 518 is also ideally suited to translating 24 bit

storage to a downstream 16 bit recording medium like DAT or CDR.

In fact, the noise-shaping options of 518 allow most of the subjective

dynamic range of a 20 bit master to be retained in the 16 bit storage

device.

Accurate DSP. The quality of signal processing used in 518 is

substantially higher than that normally found in PC editors or sound

API functions. For example, 518 uses the most sophisticated re-

dithering technology combined with 72 bit internal processing to

ensure that any level changes or equalisations are made truly

transparent to the listener. Much of this technology is proprietary to

Meridian.

RS232 control. The 518 supports direct RS232 control from a PC–

effectively turning it into a 2-channel DSP peripheral.

Customising features

As the previous sections illustrate, the 518 is very flexible. You have the

opportunity to significantly customise its functions to give you the

functionality that exactly suits your application.

The section ‘Customising 518, an overview' on page 37 describes the

options in detail.

We recommend that you first get to know the 518 using one of the

standard setups, and by working through this manual. Do not be afraid

later to experiment with customising – we have given you a simple way to

get back to where you started! (See page 23).

518 as provided has three standard configurations that we call Type

settings. Each Type gives a different set of options; this feature is

described fully on page 23.

Note By selecting a Type you automatically reset all custom settings for

518 to that default.

518 has four operating modes (not to be confused with setup Types):

Normal

Standby

Type

Config

Normal and Standby are the everyday operating modes: the basic operat-

ing instructions refer to these.

Type, and Config are used to make choices about the way 518 works.

These are described later in the section: ‘Configuring 518, an overview' on

page 37.

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Using 518 in Hi Fi Systems

Starting off with 518

Checking

Before turning on the power, check once again that you have made all the

connections correctly.

The 518 is designed to be left connected to AC power at all times and can

be run continuously.

Switching on

The power switch is located directly next to the power inlet on the right-

rear of 518.

1. Turn on the power switch at the rear of the unit. A small point on the

display should now be illuminated.

If there is no display

Check the integrity of the power connections, including any fuses in the

supply. If the display is still not illuminated, contact your dealer for help.

Memory

The 518 stores your latest settings for each Source in non-volatile

EEPROM memory and automatically returns to these settings either when

you come back to that Source, or on power-up.

The settings which are remembered for each Source are:

Gain (not volume in Control Unit mode)

DSP

Dither

Out

Standby

The entire 500 Series is designed to be left connected to AC power at all

times.

This Standby state ensures that the components operate at maximum

efficiency from the moment you start listening. It is perfectly safe and

consumes a negligible amount of power. However, when you are not

going to use your system for an extended period of time, e.g. when you

are going on holiday, we would advise you to disconnect it from the AC

power supply.

Basic operation of 518

The majority of functions are available from the front panel controls. When

used as a preamplifier (Type 0), more functions are available using the

Meridian System Remote control. See ' Advanced operation using the

Remote Control' on page 15.

This section describes the front-panel operation for those controls that are

common to all applications.

The following sections describe differences when operating 518 as a

Control unit, as a Resolution Enhancer and as a Mastering processor.

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Using 518 in Hi Fi Systems

Note 518 can be used with or without other Meridian equipment. When it

is used as the main system control unit it is normally the ‘System

Controller’ and operates exactly as described below. Systems including

other Meridian control units like 562 or 565 or DSP speakers will always

elect for 518 not to be System Controller and there are some functional

differences.

Operating 518 as a Control Unit (Type 0)

Note Do not use 518 as a Control Unit if the system has a Meridian 565

or DSP loudspeaker. (Use Type 1)

Selecting a source

1. press Source until the input you require is indicated

2. release Source

press a Source key on the Remote

Selecting a source will bring 518 out of Standby.

Adjusting the volume

To increase the volume

1. press , the right-hand volume key on the 518

press the top red key on the Remote

To decrease the volume

1. press , the left hand volume key on the 518

press the bottom red key on the Remote Control

As you adjust the volume setting, the display will change to show the cur-

rent source and volume number. For example:

would indicate that you were listening to a Compact

Disc at a volume setting of 65. The volume level dis-

played will count up or down and ranges from 1 to 99. Each step is 1dB.

Subjectively a volume increase of 9dB is equivalent to a doubling of

loudness. Each volume number represents about a 11% change in loud-

ness; nine steps to double loudness. In a traditional analogue preamplifier

using a rotary volume control the mid-way position usually offers

approximately unity gain – with full volume corresponding to around

+20dBgain.

In 518 the unity-gain i.e. 0dB setting is at volume number 87. For normal

to high-level listening you should expect volume numbers in the region 60

to 90. For this reason 518 starts at power-up with volume number 87.

Out

1. Press Out to cycle between the output word options.

The Out key is used to set the number of output bits. It is also used to set

consumer or professional channel-status output format. The choices are:

16C, 18C, 20C, 22C, 24C, 16P, 18P, 20P, 22P, 24P

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Using 518 in Hi Fi Systems

The numbers indicate the number of output bits. C and P represent the

choice of consumer and professional channel status formats respectively.

Information: 24 audio data bits are always written to the left and right

output words but the least significant bits, below the number of output bits

chosen, are set to zero.

e.g. for 16 C

16 data bits

0 0 0 0 0 0 0 0

e.g. for 18 C

18 data bits

0 0 0 0 0 0 0 0

1. Press In to cycle between the input word options.

The In key sets the number of input bits to be read from each input word.

The least significant bits below the number of input bits are masked (i.e.

ignored).

Note It is extremely important that the number of input bits is equal to or

greater than the number of data bits available on the input. If input is from

a device which is known to use some of the 24 data bits for non-audio

data or status¹, the number of input bits must be equal to the number of

input audio data bits.

Both professional and consumer channel status input signals are

acceptable to the 518.

Dither

1. Press Dither to cycle between the dither options.

Appendix 1 shows the frequency shapes of these dithers.

Flat

Flat uses additive, white-spectrum, triangular probability-distribution

(TPDF) dither.

1. Press Dither again to choose between the dither options.

HP (high-pass) uses additive, high-pass, TPDF dither.

Shape A

Shape A uses flat dither and a 2nd-order shaper optimised to MAF. ²

Shape B

Shape B uses flat dither and a 9th-order shaper optimised to MAP. ³

Shape C

¹For example, some A/D converters based on Crystal Semiconductor Ô

converters may have level information embedded below the LSB.

²MAF, Minimum Audible Field, is the appropriate threshold curve for

human listeners with normal stereo loudspeakers.

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Using 518 in Hi Fi Systems

Shape C uses flat dither and a 9th-order shaper optimised to MAF.

Shape D

Shape D uses high-pass dither and a 9th-order shaper optimised to

MAF.

Shape E

Shape E uses high-pass dither and a 2nd-order shaper optimised to

MAF.

DSP

1. Press DSP to select the primary processing mode.

The display will show:

Gain

Gain has a flat frequency response, but the level of the signal level is

adjusted using a precision dithered multiplication. All the front panel

keys are available to specify processing.

1. Press DSP again.

The display will show:

Emph

Emphasis ensures that the output of 518 is always pre-emphasised

according to the 50/15µs CD standard. 518 uses precision DSP to pre-

emphasis the signal providing the incoming signal is not already pre-

emphasised. If the incoming signal is pre-emphasised the red Emph

light indicates this.

Emphasis is the recommended mode for most program material

providing the DAC system is correctly designed and uses analogue de-

emphasis.

or:

De-Emph 87

De-Emph provides the CD de-emphasis function to very high precision

when the incoming signal is pre-emphasised. You would use this only

if you have a DAC which provides digital de-emphasis. This adaptive

mode ensures that the output of 518 is never pre-emphasised.

Note Gain functions in Emphasis and De-Emphasis, in fact all the front

panel keys are available to specify processing.

Display

1. Press Display key to select between the following display formats

Emph

Pre-emphasis option and gain setting, or

ShpB 67

Dither mode and gain setting, or

CD 67

Source and gain setting, or

³MAP, Minimum Audible Pressure, is the appropriate threshold curve for

human listeners using headphones.

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Using 518 in Hi Fi Systems

20C16

Input/output choice and gain setting, (This example indicates 20 bits of

input and 16 bits of output in consumer format), or

44k1

Sampling frequency and gain. If there is no input signal the display

would indicate no lock as follows:

N.L.

Emphasis Light

There is a light on the front panel Emph which indicates when the

channel status suggests that the incoming audio is pre-emphasised. It is

not affected by the user's settings on the 518 itself.

Clip Display

Some of the processing modes in 518 deliberately allow you to increase

the overall level of the signal. If the output signal exceeds full scale, the

518:

clips (saturates) at full code (normally sounding benign on short

overloads), and

displays a clip message like:

ClipL

The clip message will indicate whether the overload occurred on Left,

Right or both.

Clipping in DSP has nothing like the bad sonic consequences of clipping

analogue systems. Normally small amounts of clipping cannot be heard.

Software version

In Standby:

1. Press and hold Display.

The display will show the version number of the microcontroller

software, followed by the DSP version e.g.:

DSP

1.5

Advanced operation using the Remote Control

Putting the 518 in Standby

1. press Standby on the Remote Control

put another Meridian component into Standby.

Coming out of Standby

To start up the 518 from Standby

1. Select a source from the front panel or the Remote Control (MSR).

If the 518 is part of a Meridian system, bring any component out of

Standby. For example start up a Meridian CD-player.

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Using 518 in Hi Fi Systems

Muting the sound

The mute facility cuts off the sound by setting the volume level to zero.

To mute the sound

1. Press Mute on the Remote Control. The output will mute and the

display will change to:

Muted

To restore the sound

1. Press Mute a second time.

The volume level and display will be restored.

Menu Keys

When the 518 is used as a control unit and it is the system controller, then

the four menu keys on the MSR can be used to access the DSP, Dither,

In and Out menu functions.

To access a menu

1. Press w or e on the remote.

The menu will be displayed.

To change a menu

1. Press n or s on the remote.

Operating 518 as Resolution Enhancer (Type 1)

Note Do not use Resolution Enhancement mode if you want the 518 to

provide the volume control. (Use Type 0)

Volume control

The 518 does not provide the main system volume control in Resolution

enhancement (Type 1) mode.

If 518 is used with other Meridian controllers like 565 or DSP

loudspeakers, they will provide the volume function and the normal

Meridian 0–99 volume number display.

In Resolution Enhancement mode, 518 does provide a secondary gain

control which allows you to maximise the resolution of down-stream

processors and DACs by raising each piece to full digital code.

This function is called 'Gain' and does not follow the system volume

control.

Gain control

Gain control is provided in one decibel steps from +12 dB down to -99 dB.

1. Press ▲

The gain will increase in 1dB increments, and the display will show the

gain in dBs, something like:

1. Press ▼, to decrease the gain.

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Operation summary

Memory

In Resolution Enhancement mode, 518 maintains a continuous memory of

the DSP, Dither, Gain, In and Out settings for each source.

So, if you had determined that, e.g. CD should always use Gain 0dB but

that Radio could always use Emphasis and +2dB, then 518 will remember

these and automatically reconfigure itself for each source.

DSP

In addition to the DSP modes offered in Control Unit (see page 15),

Resolution Enhancement adds Bypass.

Bypass transmits all 24 bits on the input to the output without any

processing.

Note When Bypass is chosen, all the other front panel keys are disabled.

Operation summary

On the 518 front panel

Key

Action

Source

Display

Selects Source or input

Cycle the display through:

Processing option with gain in dB

Dither option with gain in dB

Input/output choices with gain in dB

Sampling frequency and gain in dB

Blank

DSP

Select main processing method: Bypass,

Gain, Emphasis, De-emphasis.

Dither

Select dither or noise shaper to be used

Set number of input bits

Out

Set number of output bits and consumer or

professional use of channel status

Decrease volume/gain

Increase volume/gain

With the Remote Control

Source keys

Selects input depending on

customisation.

Standby

Puts the 518 into the Standby

state.

Clear

Autoconfigure (in Standby)

Access the Menus

w e

Change the Menus

n s

Fn + Display

Change 518 Display

Change the primary volume.

Red n and s

Mute

Mutes output.

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Customising 518: overview

Customising 518, an overview

518 is a very sophisticated device with a huge number of options to allow

you to set up exactly the system you need or to experiment with new

possibilities.

Programming 518 is a straightforward process and you should not be

timid about experimenting. Although the setup is stored in non-volatile

memory called EEPROM, the EPROM (which you cannot change)

contains default Type settings and you can return to these at any time.

Restoring default settings

1. Switch off any power amplifiers that are connected to 518.

2. Switch off the 518 using the power switch on the back.

3. While pressing the Source key on the 518 front panel, switch the

power on again. The display will read:

Type

4. Release the Source key

At this stage you can change the Type from 0 – 2 using the n and s

Volume keys.

5. Switch off the 518 using the power switch on the back.

6. After half a second, switch the 518 power on again.

Caution Some power amplifiers are very susceptible to small surges that

may result from the process of switching a preamplifier on and off. Some

– like the Meridian 205, 555 or 605 incorporate DC-offset protection that

may be triggered by this process. Meridian active or digital loudspeakers

are inherently proof against these surges and need not be switched off. In

general digital products like power amplifiers, recorders etc. will be

unpredictable when they have the digital signal interrupted.

518 has two setup options; Type and Config. These together with Normal

and Standby give the 518 four operating states. The following sections

give an overview.

Type: an overview

Type just described, restores one of the default settings. No further

actions are possible.

Config: an overview

Config mode is used for setting fundamentals of options and control.

Consequently in Config the outputs of 518 are muted while you make the

necessary choices. The choices available in Config are outlined in the

following sections.

Config: control settings

In Config you can make selections that effect the way 518 responds to

certain keys. The main choices of this kind are:

whether the 518 is to auto-configure, or you will determine the

controller in the system.

The ‘address’ of the product.

whether or not Standby is permitted.¹

¹Standby is not recommended for 'Pro' or Mastering situations

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Customising 518: overview

whether or not the Bypass DSP option is available.²

whether or not a blank display option is allowed.

whether or not the Emphasis DSP option is adaptive – i.e. reacts to

the incoming emphasis status.

choices on how the volume control operates and displays.

Details of these are described in the next section.

Config: sources and inputs

In Config you can also make selections to do with sources, e.g.

how many inputs will be active

which sources you can select

which key on the remote control selects which source

the Logo for that input on the 518 display

the physical input connection to 518.

the Comms type of the source, i.e. whether it is a Meridian controllable

source like CD or Radio

the address for that source product

How to customise 518

The 518 comes configured in Resolution Enhancement mode (Type 1)

and needs no customising to become operational.

There are a very large number of different configurations possible. This

section tells you how to change the configuration.

Customising, general procedure

518 has four operating modes (not to be confused with setup Types):

Normal

Standby

Type

Config

Normal and Standby are the everyday operating modes: the operating

instructions refer to these.

Type and Config are used to make choices about the way 518 works.

These are described in the section: ‘Configuring 518, an overview' on

page 37.

How to change to Type or Config

To change to Type or Config you use the same basic procedure.

1. Switch off any power amplifiers that are connected to the system.

2. Switch off the 518 using the power switch on the back.

3. While pressing the specific key for the operating mode you want on the

518 front panel, switch the power on again.

518 will display a message to inform you which mode it is in.

4. Release the key

At this stage you can make the adjustments required.

In step 3, the front panel key is:

Type – press and hold Source.

Config – press and hold Display.

Normal – do not use any key!

²Bypass is not available if the 518 is the system volume control!

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Customise 518 using Type

Caution Some power amplifiers are very susceptible to small surges that

may result from the process of switching a preamplifier on and off. Some

– like the Meridian 205 or 605 incorporate DC-offset protection that may

be triggered by this process. Meridian active or digital loudspeakers are

inherently proof against these surges and need not be switched off. In

general digital products like power amplifiers, recorders etc. will be

unpredictable when they have the digital signal interrupted.

How to change back to Normal

To revert to Normal .

1. Switch off the 518 using the power switch on the back.

2. After half a second, switch the 518 power on again.

Making changes to an existing setup

Config is a configuration editing mode, it does not reset on entry. Type

however performs a full reset of all parameters.

To make any changes to your custom configuration:

1. Change to Config,

2. make the changes you want,

3. change back to Normal.

Customising using Type

Type is a mode used specifically to setup 518 into one of three factory-

preset configurations.

Type resets the following for all three Types.

Setting

Controller

System Address

Product Address

Standby

Type 0

Type 1

Type 2

Auto

N.Con

Bypass

Blank

*Emph

Volume

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Customise 518 using Type

Source-Logo-input mapping as shown below.

Source

Logo

Type 0

Input

Type 1

Input

Type 2

Input

Comms

type

Radio

–

Tape1

Tape2

CDR

Cable

Text

VCR1

VCR2

Selecting Types

1. Switch off any power amplifiers that are connected to the system.

2. Switch off the 518 using the power switch on the back.

3. While pressing the Off key on the 518 front panel, switch the power on

again. The display will read:

Type

4. Release the Off key

5. Use the front-panel and Volume keys to move the selection

between Types 0 – 2.

6. When you have the Type you want displayed, wait one second for 518

to action the choice.

7. Switch off the 518 using the power switch on the back.

8. After half a second, switch the 518 power on again to restore Normal

mode.

Customising using Config

In Config you can review and change settings to do with communications,

control and the hardware options you have. In Config you also make

choices about the number and types of sources, what the display shows

when you select them etc. The 518 is initially programmed to Type 1 and

all Types set up the source configuration as shown in the previous Tables.

How to use Config

1. Switch off any power amplifiers that are connected to the system.

2. Switch off the 518 using the power switch on the back.

3. While pressing the Display key on the 518 front panel, switch the

power on again. The display will read:

Config

4. Release the Display key, the display will show:

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Customising 518 using Config

Auto

Selecting the controller mode

In Config mode:

1. Press Display until you see a display like:

Auto

2. Use the and , Volume keys to choose between:

Auto, meaning configuring can be automatic

Cont, meaning the 518 will be the system controller

N.Con, meaning the 518 will not be the controller

Setting the system address for 518

In Config mode:

1. Press Display until you see a display like:

SA=1

This means the system address is 1. The Meridian 500 Comms system

allows for up to eight systems operating on the same network. Unless you

are setting up a Multiroom system, or are advised to do so by Meridian

support personnel, we suggest you leave this on address 1.

Setting the product address for 518

In Config mode:

1. Press Display until you see a display like:

PA=1

This means the product address is 1. The Meridian 500 Comms system

allows for up to eight products of the same type operating on the network.

Unless you are setting up a Multiroom system, or are advised to do so by

Meridian support personnel, we suggest you leave this on address 1.

Note When customisation is complete, switch the power off and then on

again to restore Normal mode and to save what you have done.

Setting the Standby mode for 518

In Config mode:

1. Press Display until you see a display like:

Stby

This means that Standby mode is available. To prevent Standby chose N.

2. Use the and , Volume keys to choose between Yes or No.

Setting the Bypass option for 518

In Config mode:

1. Press Display until you see a display like:

Bypass

This means that Bypass is available. Bypass prevents the 518 operating

as a volume control and is therefore it is highly undesirable to access it by

mistake if you are using 518 to control volume.

2. Use the and , Volume keys to choose between Yes or No.

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Customising 518 using Config

Setting the Blank display option for 518

In Config mode:

1. Press Display until you see a display like:

Blank

This means that a blank display is one of the options offered by the

Display key. To remove this option chose N.

2. Use the and , Volume keys to choose between Yes or No.

Setting the Emphasis option for 518

In Config mode:

1. Press Display until you see a display like:

*Emph

*Emph Y means that pre-emphasis will be 'forced' on the output signal

irrespective of the incoming channel status (displayed with the Emph

light). Normally Emphasis is an adaptive setting that guarantees pre-

emphasis on the output. There may be requirements in mastering where

pre-emphasis needs to be applied even though incoming emphasis is

indicated.

'*Emph N' means use the adaptive method.

2. Use the and , Volume keys to choose between Yes or No.

Chose 'Y' to over-ride the incoming emphasis flag¹.

If in doubt chose 'N'. '*Emph Y’ is not needed in normal use.

Setting the Volume mode for 518

In Config mode:

1. Press Display until you see a display like:

Vol.

In the 500 Comms system there is provision for two volume controls, main

and secondary.

2. Use the and , Volume keys to choose between:

N. No means that the gain control in 518 is independent of any

other Meridian components in the system and is stored by Source.

M. Volume Main means that the volume control in 518 will follow

the main Meridian system and respond to the red keys on the

remote.

S. Volume secondary means that the volume control in 518 will

follow the second volume control in the system and respond to the

shifted volume command on the remote. (Fn + Volume)

For further details on shifted commands see the manual supplied with the

remote control.

If in doubt choose VolM for a preamp and N for Resolution Enhancement.

Setting the Volume display

In Config mode:

1. Press Display until you see a display like:

¹Note. *Emph also allows De-emphasis of a signal not shown to be

emphasised.

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Customising 518 using Config

Vol.

The gain of 518 can either be displayed in absolute dB in the range -99dB

to +12dB, or as a Meridian volume number 0 to 99 – where 87

corresponds to 0dB.

2. Use the and , Volume keys to choose dB or ##.

Setting up sources

For each of the twelve source selection keys on the Remote control you

choose a display Logo and a physical input connection.

Normally as shown, we set the CD key to give a CD display with the D1

(Digital 1) input selected. You may however wish to display CD1 for your

main CD player and to connect it to D2.

A full list of possible logos and their meanings is:

Source

Logo

Source

S-VHS

Betamax

Camera

Video 8

CD-V

Logo

Source

DAB

Logo

DAB

DSat

ADC

Reel

Radio

Dig. Sat

ADC

Tape 1

Tape 2

CDR

R-Reel

CD-V

CD-I

CD-T

FM tuner FMTun

AM tuner AMTun

MW tuner MWRad

CD-I

Cable

Teletext

VCR 1

VCR 2

CD-T

CD Photo CD Photo SW tuner SWRad

CD Lib CD Li LW tuner LWRad

CD Jbox CD Jbox Line

CD-ROM CD-ROM Mic.

Line

Mic

Laserdisc LD

Satellite

CDX

DAT

Aux

DCC

Mixer

Simul.

Mixer

Simul

78 rpm

VHS

78 rpm

Phono

Minidisc

Phono

Mdisc

Computer PC

Choosing source logos

Note at any time in the source configuring process you can use the front-

panel Display key or the handset Mute key to return to the root menu

with a display like ‘Auto'.

In Config mode:

1. Press Source until you see a Remote-key (source) + logo display like

2. Press Source until the Remote key name for the source you wish to

configure is displayed.

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Customising 518 using Config

3. Use the and Volume keys until the correct logo is indicated – see

the list above.

4. Make changes for all the source options.

Note If you select the logo ‘N’ the 518 will ignore that key on the Remote

control and that source will not be offered in the Normal source menu.

Changing the input for a source

In Config mode:

1. Press Source until you see a Remote-key (source) + logo display like

2. Press Source until the Remote key name for the source you wish to

configure is displayed.

3. Press DSP.

you should see the display change to one like:

The Remote control key you are setting up is the source name and it is

indicated on the left as before. Now the letters on the right indicate which

of the four physical input connectors will be selected.

To change the physical inputs:

1. Use the and Volume keys until the correct one is indicated

2. Make changes for all the source options by pressing Source.

Note When customisation is complete, switch the power off and then on

again to restore Normal mode and to save what you have done.

Choosing the Comms type for a source product

This setting currently only applies to a source which is a Meridian CD

player or Radio tuner.

In Config mode:

1. Press Source until you see a Remote-key (source) + logo display like

2. Press Source until the Remote key name for the source you wish to

configure is displayed.

3. Press DSP until you see a display like:

4. Use the and Volume keys to chose the Comms type.

CD players are always 1C, tuners are always 2C. NC means the source is

not Meridian.

5. Make changes for all the source options by pressing Source.

Choosing the address of a source product

In Config mode:

1. Press DSP until you see a display like:

2. Use the and Volume keys to choose the product address

3. Make changes for all the source options by pressing Source.

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Connecting 518

Connections

There are three types of connection that need to be made to the 518.

power, see page 14.

digital audio, see page 40.

communications, see page 30.

Digital audio connections

Digital connections are made:

from the digital outputs of 518 to your digital power amplifiers, digital

loudspeakers, digital recording devices, editors.

to the digital input of 518 from sources like CD, A/D converters,

mixers, digital recording devices, editors.

Digital connections should be made with either:

high-quality 75W screened cable on SPDIF

high-quality 110W balanced screened cable on AES/EBU.

For advice on the type of cable we suggest you consult your dealer and

the manual supplied with the source equipment.

Meridian has a range of suitable digital interconnects available as

accessories. We recommend you do not use cables intended for analogue

connection since these do not usually have the degree of shielding or an

impedance of 75W. Cable intended for UHF applications like antenna

down-lead is also unsuitable since it does not shield adequately in the 1–

30MHz region.

Warning. We strongly recommend the use of well-screened precision

coaxial cable. Certain ‘audiophile' cables are not screened. Screened

cable will minimise RF interaction with your system. Unscreened cables

for digital connections may cause illegal levels of RF interference.

Digital input connections

1. Make digital connections from each of your digital sources to an

appropriate digital input on 518. The digital inputs on 518 are labelled:

D1 to D3 for the three cable inputs, and

OP for the optical input.

These inputs are identical in performance and are assigned in Config.

D1 also has an AES/EBU connection. Only one can be used at a time, i.e.

D1 is either SPDIF or AES/EBU not both.

Digital output connection

1. Make digital connections from the output to the equipment you have

chosen to follow it.

You can use both the SPDIF and AES/EBU output connections at the

same time.

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Connecting 518

Communications connections

Communications connections are only made to other Meridian equipment.

The following sections describe the major points.

To connect to other Meridian 500 Series equipment

1. Connect one of the COMMS sockets on the rear panel of the 518 to

one of the COMMS sockets on another 500 Series unit, using the 500

Comms lead supplied.

2. Connect all the 500 Series products together in this way to form a

chain (not a loop). The order in which they are connected is not

important.

If the system is to operate in 500 mode, then, configure the units with the

following automatic setup procedure.

1. Switch all the units to Standby.

2. Press Clear on the handset.

Each unit will display:

Auto

One unit will then be designated as the controller and display:

Con

All the other units will be configured as non-controllers and display:

NCon

The system is now set up and ready to use.

If for any reason the automatic setup does not give the configuration you

want, you can restore the default operation by selecting a Type or by

setting the controller status in Config as described on page 21.

Connecting to Meridian Digital speakers

1. Connect the phono plug on the end of the M-lead to the digital output

of the 518.

4. Connect one of the two DIN plugs on one end of the M-lead to one of

the COMMS sockets on the back of 518.

Note There are usually two DIN plugs on an M-lead. Take care to chose

the correct one and do not force the plug. The second plug is used to

connect to any 200 Series products in the range.

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Using 518 for Mastering and Multimedia

Part 2

Mastering Processor

The Meridian 518 Digital Audio Processor has been designed to allow

the making of better recordings, and in particular to enable the

production of high-quality, enhanced-definition CDs.

The predominantly available channels for delivering high-quality sound

to consumers is stereo, linear-encoded 16 bit PCM. There is also no

realistic prospect of a widely-available improvement on this capability.

While CD is limited to 16 bits, we now have A/D converters, recorders

and editors operating with anywhere between 16 and 24 bit words.

The Meridian 518 provides the very best quality and combination of

signal-processing functions for use when preparing material for issue on

media like CD. In fact, using the unique signal processing in 518, CDs can

be produced with up to 19-bit subjective dynamic range.

The functions of 518 have been optimised for use in three stages of

the production process, namely:

on location, processing the signal between the A/D converter and

recorder,

during transfer of a recording to an editor,

during transfer from editor to production master.

In each such step, the word-size can be different, and 518 can make

these processes optimal.

The signal-processing used is based on an extensive programme of

research, and is implemented in DSP with an internal precision of 72

bits to ensure exceptional transparency. For a very full technical

background, please see the papers referred to below: copies may be

obtained from Meridian. ^{1 2 3 4}

518 also finds applications in professional or consumer replay

situations. Here the precision gain control and pre/de-emphasis

processing can replace the system preamp and enhance the dynamic

range of a D/A converter – see the earlier sections of this manual.

¹J.R. Stuart and R.J. Wilson, "A Search for Efficient Dither for DSP

Applications", 92nd AES Convention, Vienna 1991, Preprint #3334

²J.R. Stuart, "Noise: Methods for estimating Detectability and Threshold", 94th

AES Convention, Berlin 1993, Preprint #3477

³M.A. Gerzon, P.G. Craven, J.R. Stuart, R.J. Wilson, "Psychoacoustic Noise-

Shaped Improvements to CD and other Linear Digital Media", 94th AES

Convention, Berlin 1993, Preprint #3501

⁴J.R. Stuart and R.J. Wilson, "Dynamic Range Enhancement Using Noise-

Shaped Dither Applied to Signals With and Without Pre-emphasis", In

preparation for AES Convention, Amsterdam 1994.

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Using 518 for Mastering and Multimedia

Description

The Meridian 518 Digital Audio Processor is a general-purpose digital-

domain DSP engine that operates on or between consumer or

professional interfaces at sampling frequencies between 32–50kHz and

with up to 24 bit input and output.

The supplied user programmes are intended for use in recording, editing,

mastering and replay situations.

The primary functions of 518 permit the correct signal processing when

moving between carriers or channels of different word size. Options are

also offered – in the form of noise-shaping, gain control and precision pre

and de-emphasis – to maximise the subjective dynamic range of the final

carrier or channel. Typical applications would be to use 518 at all stages,

i.e. between an A/D converter and a recorder; then between the recorder

and any editor; and finally between the editor and the final carrier.

518 has been extensively beta-tested, there are many highly-regarded

commercially-available CDs that have used its processes.

518 as a Mastering or Multimedia Processor (Type 2)

This section covers unusual features of 518 operation when used in

mastering or Multimedia processor mode (Type 2). Please refer to the

normal operating instructions on page 15 for more details.

Meridian 500 Comms warning

We strongly recommend that you do not connect anything to the Comms

sockets in Type 2. The behaviour of the 518 may be unpredictable.

If you want to use 518 as a Mastering or Multimedia Processor along with

other Meridian equipment, we suggest you start from Type 1 and build the

appropriate functionality in Config.

Emphasis Light

There is an Emph light on the front panel which indicates when the

channel status suggests that the incoming audio is pre-emphasised. It is

not affected by the user's settings on the 518 itself. Obviously in this

circumstance, it is not advisable to pre-emphasise again using 518!

Routinely 518 prevents you from making this mistake, however, against

the possibility that the incoming channel-status may be wrong, you can

over-ride this protection, see *Emph on page 26.

Selecting a source

1. press Source until the input you require is indicated

2. release Source

Gain control

Gain control is provided in one decibel steps from +12 dB down to -99 dB.

1. Press ▲

The gain will increase in 1dB increments, and the display will show the

gain in dBs, something like:

1. Press ▼, to decrease the gain.

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Using 518 for Mastering and Multimedia

Memory

In Mastering Processor mode, 518 maintains a continuous memory of the

DSP, Dither, Gain, In and Out settings for each source.

So, if you had determined that, e.g. D1 is an 18 bit source that should

always use Gain 0dB but that D2 is 16 bit and can always use Emphasis

and +2dB, then 518 will remember these and automatically reconfigure

itself for each source as you switch between them.

DSP

1. Press DSP to select the primary processing mode.

The display will show:

Bypass

Bypass transmits all 24 bits on the input to the output without any

processing.

Note When Bypass is chosen, all the other front panel keys are disabled.

1. Press DSP again.

The display will show:

Gain

Gain has a flat frequency response, but the level of the signal level is

adjusted using a precision dithered multiplication. All the front panel

keys are available to specify processing.

1. Press DSP again.

The display will show:

Emph

Emphasis ensures that the output of 518 is always pre-emphasised

according to the 50/15µs CD standard. 518 uses precision DSP to pre-

emphasis the signal providing the incoming signal is not already pre-

emphasised. If the incoming signal is pre-emphasised the red Emph

light indicates this.

or:

De-Emph 0

De-Emph provides the CD de-emphasis function to very high precision

– providing the incoming signal is emphasised (Emph light on).

Note Gain functions in Emphasis and De-Emphasis, and all the front

panel keys are available to specify processing.

Display

1. Press Display key to select between the following display formats

Emph

Pre-emphasis option and gain setting, or

ShpB +2

Dither mode and gain setting, or

CD +2

Source and gain setting, or

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20C16

Input/output choice and gain setting, (This example indicates 20 bits of

input and 16 bits of output in consumer format), or

44k1

Sampling frequency and gain. If there is no input signal the display

would indicate no lock as follows:

N.L.

Clip Display

Some of the processing modes in 518 deliberately allow you to increase

the overall level of the signal. If the output signal exceeds full scale, the

518:

clips (saturates) at full code (normally sounding benign on short

overloads), and

displays a clip message like:

ClipL

+10

The clip message will indicate whether the overload occurred on Left,

Right or both.

Clipping in DSP has nothing like the bad sonic consequences of clipping

analogue systems. Normally small amounts of clipping cannot be

detected.

Making Recordings

Case 1. The recording is made to the final carrier, DAT or CDR

at 16 bits

a) 16-bit A/D – 518 – CDR, use Bypass.

b) 20-bit A/D – 518 – CDR.

use Emphasis (if the material has sufficient headroom at high

frequencies), or:

use Gain (on the maximum setting which does not cause clipping)

with:

Shape B, C or D.

In set to 20.

Out set to 16 C (possibly 16 P).

Case 2. The recording will be further processed: carrier and

A/D converter have the same word size

In this case use Bypass.

Case 3. The recording will be further processed: carrier has

more bits than the A/D converter

In this case use Bypass.

Case 4. The recording will be further processed: the carrier

has fewer bits than the A/D converter

Use Emphasis if the material has sufficient headroom at high

frequencies, or:

use Gain on the maximum setting which does not cause clipping.

In both cases, also select:

Flat or H.P. dither. You may also use Shape A.

In set to the number of bits in the A/D converter.

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Out set to the number of bits in the recorder.

Transfer to editor

Case 5. The recording and editor are the same word size

In this case use Bypass.

Case 6. The recording has fewer bits than the editor

In this case use Bypass.

Case 7. The recording has more bits than the editor

In this case use Emphasis (if the recording is not already pre-

emphasised) and if there is sufficient headroom at high frequencies, or:

use Gain on the maximum setting which does not cause clipping.

In both cases, also select:

Flat or H.P. dither. You may also use Shape A.

In set to number of bits on the recording.

Out set to the number of bits used in the editor.

Transfer to the final carrier

Case 8. Editor and final carrier have same word size.

In this case use Bypass.

Case 9 Editor has fewer bits than final carrier

In this case use Bypass.

Case 10 Editor has more bits than final carrier

In this case use Emphasis (if the recording is not already pre-

emphasised) and if there is sufficient headroom at high frequencies, or:

use Gain on the maximum setting which does not cause clipping.

In both cases, also select:

Shape A, B, C or D.

In set to number of bits on the output of the editor.

Out set to the number of bits on the final carrier.

Note In this circumstance, the editor should be set to put out the

maximum number of bits it can to preserve linearity.

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About the Noise Shapers

Noise shaper characteristics

Each noise shaper presents a different degree of subjective noise

reduction – we call that its ‘advantage’ – compared with normal dithering

using white TPDF dither. Each shaper also has a different degree of HF

boost. The parameters are summarised in the table below.

Shaper

Advantage

44.1kHz

Pre-emphasis

48kHz

Pre-emphasis

Normal

0.0dB

Normal

0.0dB

Flat TPDF

High-pass

Shape A

Shape B

Shape C

Shape D

3.4dB

3.5dB

6.4dB

19dB

7.0dB

3.5dB

6.4dB

19.6

7.0dB

12.2dB

22.6dB

17.9dB

21.5dB

12.2dB

23.6dB

21.4dB

23.5dB

15.1dB

15.3dB

18.6dB

19.9dB

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Additional technical information

518 Operating Background

Transparency in digital systems

Digital audio gives a unique opportunity to deliver exceptional sound

quality in a recording or broadcast. In the first decade of this technology,

considerable progress was made developing the gateways – i.e. A/D and

D/A conversion. The promise of digital audio is only deliverable if the

digital audio signal is handled with complete integrity.

It is has been a common misconception among practising engineers that

the signal is robust once it is in the digital domain. This combined with a

general misunderstanding about dither, has led to working practises that

degrade the potential of the recording. Obviously, it is necessary to

understand the signal processes, and to have a way to process the signal

optimally.

The 518 allows you to achieve a transparent channel with the maximum

subjective dynamic range. This section explains the technical background.

Digital Audio and Quantisation

Digital audio is used because it is possible to transmit the data through

space (broadcast) or time (recording) without any loss of information or

generation degradation. This property of digital audio makes it extremely

attractive. The major development in digital audio has been in extending

our comprehension of the processes of digitisation and reconstruction of

the original analogue signal.

Dither

Dither is an essential lubricant if a digital audio channel that includes

processing is to remain transparent.

Transparency in a digital channel is the result of maintaining linearity at both

high and low levels and not falling prey to signal-processing distortions like,

for example, noise modulation.

It is well established that in order for linearity to be maintained, dither

must be applied at every non-trivial signal processing stage. By non-trivial,

we include all operations that modify a sample. With very few exceptions,

arithmetic operations that modify a sample result in an increase in the

number of bits representing the output result; in a fixed size channel, this

can therefore lead to truncation or quantisation effects.

In a recording process, the typical non-trivial operations will be:

Truncation and requantisation if the A/D converter has a larger word

size than the recorder.

Truncation and requantisation if the recorder has a larger word size

than the editor.

Truncation, requantisation and many potential signal-processing

errors in the editor itself.

Truncation and requantisation if the editor has a larger word size than

the final carrier.

Truncation and requantisation mastering house processes the

material (e.g. gain shift, dc filtering etc.).

It is well established that applying dither with triangular probability

distribution of ± 1 LSB to a quantisation process results in perfect

linearity, contributes no noise modulation and permits resolution of signal

elements below the LSB. It is therefore the ideal tool to achieve

transparent processing.

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Unfortunately, although this process is generally understood, it is not

common practise to employ correct dithering procedures at these stages.

In fact, practising engineers are often under the misapprehension that

dither is only needed once in a system, or that if there is sufficient noise in

a recording then further dither will not be needed. This is an important

misunderstanding that has so often led to lost quality in recordings.

518 provides two additive triangular probability-distribution dither forms –

flat and high-pass. The essential difference between them is that H.P.

dither has a lower subjective noise-floor, being about 3.5dB less audible

than additive white dither.

Both spectra are illustrated in Appendix 1.

Noise Shaping with dither

Noise-shaping is a technique in which a filtered version of the quantisation

error plus dither is fed back and subtracted from the quantiser input. By

this technique, the total noise can be redistributed, moving the noise from

spectral regions where the listener is sensitive to other regions where they

are less audible.

In 518 we provide four different shapers; they are carefully selected for

their different properties, each optimised for a different application.

Dynamic Range

The dynamic range of a digital channel is defined by the maximum level –

often referred to as full-scale or 0dBFS – and by the quantisation noise

floor which is itself determined by the sample word-length. A normal

TPDF dithered quantisation introduces a benign uncorrelated addition to

the noise-floor.

A background to this and a method of calculating dynamic range is given

in the paper [2] referred to on page 31 of this manual.

From a users point of view, the noise-floor is determined by the number of

bits; the subjective noise-floor is determined by the spectrum of the noise,

i.e. the shaper used.

The most important application where maximising subjective dynamic-

range occurs is in a word-size reduction. Here the correct strategy for

maximising dynamic range is to use the Gain feature of 518 to raise the

overall recording so that it nearly reaches full-scale. (This can be done by

playing the recording and monitoring with a peak-hold indicator the

maximum level; then replay increasing the gain sufficient to raise the peak

to say -1dBFS).

Further maximising of the subjective dynamic-range can occur by

minimising the impact of the added noise using a shaper. For example, if

a 20-bit original recording achieved a peak level of -4dBFS, then

transferring it to a CD using Gain +3dB and Shape B could result in a 19-

bit subjective dynamic range on the CD. Transferring it without 518, i.e. by

truncation, will reduce the recording to 15 bit with unpleasant low-level

artefacts.

Pre and De-emphasis

The use of pre and de-emphasis as signal-processing means of

optimising the subjective dynamic range of analogue channels, should be

quite familiar ideas to audio engineers. In particular, pre and de-emphasis

have been used in channels where the analogue noise level showed an

increasing level with frequency, e.g. magnetic tape, shellac or vinyl

grooves and Frequency Modulation. In all these cases, a well-

documented property of music and speech is exploited, namely that for

material microphoned at normal listening positions, and of acoustic

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Additional technical information

source, the average and peak spectrum level declines with frequency

above a few kHz. Best use is therefore made of the channel by pre-

emphasising high-frequency signals to an extent where they are more

likely to occupy the capacity of the channel. De-emphasis is applied on

replay or reception and has the dual benefit of reducing noise and

distortion from the preceding chain.

So far, all linear PCM standards used for digital audio permit the use of

pre and de-emphasis; the universal characteristic being 50/15uS.

Probably this standard came into play originally because it helped to

alleviate the very real problems of linearity in early A/D and D/A

converters.

More recently, the use of pre-emphasis has been neglected in digital

audio. The main reasons for this being:

prejudice based on the very considerable difficulty of designing a

transparent analogue pre-emphasis module in a microphone

preamplifier.

the much-improved quality of A/D and D/A converters.

the availability of A/D conversion with more significant bits than the

distribution channel (e.g. CD 16 bits).

This trend is mistaken, and for suitable material and conditions, a very

real benefit can be obtained using pre-emphasis. The improvements with

518 are unique since the noise-shaping is designed for that circumstance

and the pre-emphasis is effected in the DSP.

If we used pre-emphasis on the example of the previous section, the

resulting CD could have a subjective dynamic range of 20 bits.

Simple rules for using 518

This section lays out some simple rules for using 518 in three different

circumstances.

A step-down in sample word size

A step-down in sample word size while applying noise-shaping to give the

channel a subjective dynamic range as close as possible to the input data.

Such applications include transferring e.g. 20 bit masters to a 16 bit

carrier like CD. In these cases:

Use Gain to bring peak level as close to full-scale as possible

If the programme material permits, use pre-emphasis

Use Shape B, C or D unless there is to be significant subsequent

editing – in which case use either Shape A or high-pass dither.

No change in sample size

Modification of a signal in a channel where the same number of bits are

used to define the input and output data. In this case we should be

concerned with minimising the impact on the subjective dynamic range of

the output signal. In these cases:

Use Gain to bring peak level as close to full-scale as possible

If the programme material permits, use pre-emphasis

Use Shape A or high-pass dither.

Step up in dynamic range

Shifting incoming data to allow the output to have potential for a

subjective dynamic range that exceeds the input data without increasing

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the dynamic range of the signal itself. A typical application may be a full-

range DSP volume control, where e.g. a 16 bit input is modified by a gain

control function and passed out to a DAC of 18 or 20 bits. In these cases:

If the programme material permits, use pre-emphasis

Use Shape A or high-pass dither.

Additional technical information

Specification

Inputs

3 cable and one TOSLINK optical.

Digital serial interface to AES/EBU or SPDIF

2 channels up to 24 significant bits

Digital serial interface to AES/EBU or SPDIF

2 channels up to 24 significant bits.

32kHz – 48kHz.

Outputs

Sampling Frequency

Twin PLL

Second phase-lock loop minimises jitter at

44.1kHz to approx. 3pS rms.

Input word selection

16, 18, 20, 22, 24 bits

Output word selection 16, 18, 20, 22, 24 bits

Channel status

Dither options

Output selectable professional or consumer

Additive white spectrum TPDF

Additive high-pass spectrum TPDF

5 specific types offered, optimised for each

sampling frequency, with and without pre-

emphasis and for MAF and MAP hearing

thresholds.

Noise shapers

Processing

Gain control in 1dB steps from +12 to –99dB

Digital-domain pre-emphasis

Digital-domain de-emphasis

Accuracy

Display

72 bit internal precision

Gain, processing mode, dither, incoming

emphasis, clipping.

Digital Subcode

Channel status only

Controls

Dimensions

Weight

Source, Display, DSP, Dither, In, Out, Gain

325 x 100 x 320mm, (12.9 x 3.9 x 12.6")

5 kg (10 lb.)

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Support information

Help!

Standby point not lit

Check the following:

1. There is AC power connected to the socket on the rear of the 518

2. The power switch on the rear panel of the 518 is turned on

If the 518 will still not illuminate, check any fuses in your power supply

and the fuse in the inlet of the 518. If these are all intact, contact your

dealer.

Audible hiss at high volume settings

The input dynamic range of any recordings you have are at maximum 16

bit. The reason for this is that CD and other consumer sources use a 16

bit standard. The analogue sources you have cannot achieve this kind of

range. For comparison, analogue sources are likely to be of the order of:

FM Radio, 13 bits

Reel-reel tape, 13 bits

Cassette tape, 12 bits

LP, 11 bits.

Note that there may be a difference between the dynamic-range of the

source channel when it is operating, and the noise you hear in Standby.

For example LP normally has lower noise when the stylus is not in the

groove; similarly tape will be quieter when it is stopped. CD may also be

quieter when it is stopped, producing so-called ‘digital silence’.

The 518 has a 16 bit capability from input to output on analogue sources.

When the volume is turned up high you may hear this dither as a hiss

when the sources are stopped. This hiss is lower than the background

noise of your recordings and is of no consequence.

No output with Meridian 565, DSP speaker or DAC

Many consumer products will mute when fed a signal in Professional

format. If you have no sound – try setting Out to C.

No time display with Meridian DSP speaker

518 removes unnecessary subcode as a method of reducing jitter and

therefore improving sound quality.

Because 518 does not pass on subcode, the time display feature on

DSP5000 or DSP6000 becomes disabled. However the Meridian Comms

system keeps the speaker updated on the current track number.

Communications not working between 518 and other

Meridian products.

If you have this problem check the connections carefully.

Are you using a mix of 200 and 500 mode units?

Radio interference

NOTE 518 is a digital audio and computing device which has been de-

signed to very high standards of electromagnetic compatibility.

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FCC WARNING: This equipment generates and can radiate radio fre-

quency energy and if not installed and used correctly in accordance with

our instructions may cause interference to radio communications or radio

and television reception. It has been type-tested and complies with the

limits set out in Subpart J, Part 15 of FCC rules for a Class B computing

device. These limits are intended to provide reasonable protection against

such interference in home installations.

If this equipment does cause or suffer from interference to/from radio or

television reception then the following measures should be tried:

1. Reorient the receiving aerial (or antenna) or route the antenna cable of

the receiver as far as possible from the 518 and its cabling.

2. Ensure that the receiver uses well-screened antenna cable.

3. Relocate the receiver with respect to the 518.

4. Connect the receiver and this product to different AC outlets.

5. If the problem persists contact your dealer.

EEC This product has been designed to comply with the limits set out in

EN55013 and EN55020C.

REMEMBER to switch all units off before changing any connections.

Cleaning

When cleaning the 518 bear in mind that the front of the unit is plastic,

and the display panel and top surface are glass.

Disconnect the power cord before cleaning the unit.

Note Do not use abrasive cleaners on any part of the 518.

Maintenance & Service

The Meridian 500 Series of hi-fi components have been carefully de-

signed to give years of untroubled service, and there are no user-service-

able parts inside the case, nor do the units require any form of mainte-

nance.

In the unlikely event that your 518 fails to function correctly, it should be

returned, in its original packing, to your Meridian dealer. In case of diffi-

culty within the UK or USA please contact our sales and service offices

shown on page 4.

Outside the UK: contact the importing agent for the territory. A list of

Meridian agents abroad is available from the above address.

No responsibility can be accepted for the 518 whilst in transit to the fac-

tory or an agent and customers are, therefore, advised to insure the unit.

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Appendix 1 – Noise Shapes

Part 3

Appendix 1 – Noise Shapes

The graphs in this appendix show the relative noise spectra in dB for the

different shapers, compared with the flat-spectrum dither level for the

same word-size.

20dB

0dB

-20dB

0Hz

5kHz

10kHz

15kHz

20kHz

25kHz

Above: noise spectrum using High-Pass additive TPDF dither at 44.1kHz

10dB

5dB

0dB

-5dB

-10dB

-15dB

0Hz

5kHz

10kHz

15kHz

20kHz

25kHz

Above: noise spectrum for Shape A at 44.1kHz.

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Appendix 1 – Noise Shapes

40dB

30dB

20dB

10dB

0dB

-10dB

-20dB

-30dB

0Hz

5kHz

10kHz

15kHz

20kHz

25kHz

Frequency

Above: noise spectrum for Shape B at 44.1kHz

30dB

20dB

10dB

0dB

-10dB

-20dB

-30dB

0Hz

5kHz

10kHz

15kHz

20kHz

25kHz

Above: noise spectrum for Shape C at 44.1kHz

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Appendix 1 – Noise Shapes

40dB

30dB

20dB

10dB

0dB

-10dB

-20dB

-30dB

0Hz

5kHz

10kHz

15kHz

20kHz

25kHz

Above: noise spectrum of shape D at 44.1kHz.

Above: noise spectrum of shape E at 44.1kHz.

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Appendix 2 – Hints on Mastering

Appendix 2 – Hints on Mastering with noise-shaping

There are a few difficulties associated with employing noise-shaping

schemes to maximise the subjective dynamic-range of a digital audio

channel. These are now reviewed.

Vulnerability of the signal

The available dynamic range in a channel is only as wide as the

narrowest step. No matter how much care is taken with a recording, or to

maintain the maximum word-size right up to a noise-shaped dithered

truncation to e.g. 16 bits, the whole benefit can be thrown away if at that

stage a non-dithered signal process is carried out on the material. This is

not unheard of, a mastering house may e.g. choose to pass the signal

through an undithered dc filter!

This caution simply says that every process on the signal leading up to

delivery to the customer has to be reviewed for its impact on the noise-

floor and transparency. Such errors will be cumulative, but just one will

destroy any dynamic-range enhancements.

Audible results of digital errors and editing

Normal digital channels have provision for error detection and correction.

In sophisticated apparatus, short bursts of erroneous samples are

interpolated to reduce the audible effect. It is becoming more common in

CD replay systems, that the only error handling is a first-order hold; that is

when the system detects an erroneous sample, the previous valid sample

is output in its place.

This trend has partly been a response to the fact that errors on CD tend to

be single missing samples at an acceptably low rate. There are however

marked variations in this performance between players.

On normal music this strategy results in a minor modification to the

waveform and it usually passes unnoticed. The introduced sample is of

similar size to the signal, and is therefore readily incorporated or masked.

On normal material we also notice that errors occurring in silent passages

result in near-zero additions which tend to be inaudible.

Let us now consider the circumstance where a signal has been passed

through a noise-shaper with a function like Shape D. In loud passages

errors will be masked just as the normal circumstance. However channel

errors occurring in quiet or silent passages will tend to result in an audible

click (since the HF noise is boosted) with little or no material to mask it.

A similar problem pertains to editing ‘shaped’ material in quiet passages.

The requirement exists to maintain apparent continuity in the shaped

noise. We have observed clicks due to replay errors when shaped

material is re-played on cheap CD players, but no difficulty at all on

reasonable or up-market units.

Requirements for D/A conversion

Noise-shaping can be used to extend the audible dynamic range of a

channel beyond that which would be expected for a normal digital channel

of the same word-size. The essential principle by which this is achieved is

representing numbers below the LSB as an average of successive

bracketing numbers. For this system to work, the channel must exhibit

differential linearity equal to the resolution required.

We can illustrate this best by example. Let us assume that a signal has

been encoded with 20-bit precision and that a shaper type D has been

used to convey this signal onto a 16 bit CD channel. Measurement in the

digital domain shows very clearly the success with which the subjective

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Appendix 2 – Hints on Mastering

dynamic range is extended. Implicit in this theory is the fact that the digital

channel has near-infinite differential linearity, i.e. each bit has a magnitude

precisely twice or half the magnitude of the next.

When this signal is applied to a D/A converter some problems may arise.

First the D/A process may be associated with an oversampling digital

filter. Commonly these parts take no precautions with regard to dither and

introduce a quantisation noise-floor themselves at the approximate level

of the LSB in the filter, thereby obliterating lower-level information in the

signal. Secondly the D/A converter will not have perfect differential

linearity – there is no longer any reason why successive bits will maintain

a precise 2:1 ratio. The effect of this is also equivalent to quantisation at

the linearity level of the converter.

In summary therefore, the wide subjective dynamic range inherent in the

recording cannot be reproduced unless the replay D/A system has both a

word-size (in terms of associated oversampling filters) and a differential

linearity equivalent to the original material, which in this example was 20

bit. The result would be further improved by the correct use of dither and

noise-shaping in the digital filter.

That a subjective channel dynamic range of approaching 20 bit can be

conveyed on a 16 bit channel is quite remarkable. On reflection, it should

not be surprising that to realise this benefit, both the A/D and D/A sub-

systems must have the required 20-bit precision.

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Appendix 3 – RS232

The 518 may be operated via its RS232 interface.

Set the communication settings as follows:

Baud rate 9600

Data bits 8

Stop bit 1

Parity none

The 518 is operated by sending short command strings on the RS232

interface. Each command is terminated by a <return> (dec. 13). No echo

is implemented. Any subsequent <return> on its own repeats the last

command.

518 returns useful strings acknowledging the command and giving status

information.

Handset Functions

The following commands emulate the MSR remote control keys.

Sources send one of: CD, RD, LP, TV, T1, T2, CR, CB, TX, V1, V2, LD

Numbers send one of: N1, N2, N3, N4, N5, N6, N7, N8, N9, N0, DP

(decimal point)

Menus send one of: ML, MR, MP, MM (for w, e , n, s .)

Source send one of: PR (previous), PL (play), NE (next), PS (pause), FB

(fast back), ST (stop), FF (fast forward), RC (record), RP (repeat)

Memory: SR (store), CL (clear)

Status: DI (display), SB (standby)

Volume: VP (up), VM (down), MU (mute)

GoTo Functions

There are direct access functions that use two-character codes that may

be followed by additional numbers or parameters.

VN##

GN±##

Goto volume number

Goto gain number

Goto DSP Bypass

Goto DSP Gain

Goto DSP Emphasis

Goto DSP De-emphasis

Goto dither # (0=flat, 1= HP, ....6=ShapeE)

Goto input bits ##

DT#

IN##

OU##C

OU##P

Goto output bits ## (Consumer format)

Goto output bits ## (Professional format)

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Appendix 4 –Resolution Enhancement

Resolution enhancement in 518 depends on six techniques.

1. De-jittering

2. Dynamic-range optimisation with Gain

3. Dynamic-range optimisation with Pre-emphasis.

4. Dynamic-range optimisation with Noise-shaped Dither.

5. DAC enhancement by using high-frequency dither.

6. DAC or channel enhancement by word-length matching.

Jitter and de-jittering

Digital audio works by representing the acoustic waveform by a series of

evenly-spaced sample words. In digital-audio systems, it is quite possible

– in fact usual – for the data to pass without error. Unfortunately, where

the data is passed from process to process, the exact even timing of the

samples may become disturbed so that the samples arrive occasionally

slightly early or late. inaccuracy in the timing of the incoming stream is

called 'jitter' – and Meridian have been skilled at dealing with this since

1983.

When a jittered digital stream is fed to a DAC, the sound is degraded –

typically a listener will describe it as 'harsh', 'glassy' or 'bright' or lacking in

'spaciousness'.

The de-jittering element is of great importance to some CD players, and of

enormous significance to any LaserDisc player as they tend to have

relatively high-jitter output. If you want to use a LaserDisc player for

serious CD listening, then the de-jittering in 518 is absolutely necessary.

Another interesting aspect of jitter is that the current AES/EBU and SPDIF

interfaces use coding that causes some signal-dependent jitter to be

introduced. So, we can de-jitter a stream, but if it is then passed through a

series of digital interfaces then it will almost certainly benefit from de-

jittering again. Now, jitter does no harm in the digital domain: it is only

important that the stream be correct going into the final converter – which

in a Meridian system may be a DAC like 563, a Surround Processor like

565 or a DSP loudspeaker.

Figure 1. Showing jitter spectrum of twin PLL.

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Appendix 4 –Resolution Enhancement

The block diagram on page 7 shows the twin phase-lock-loop which 518

uses to smooth out the digital sample stream. Each loop acts as a

progressive 'flywheel' – following the average sample rate exactly – but

removing short-term speed unevenness.

Dynamic-range

The dynamic range of a channel or system is determined by the ratio

between the loudest signal it will carry without distortion and the

background noise.

For digital signals the loudest signal – full output of the channel – is called

full-scale and this level uses all the available bits.

In a system using digital components, the background noise may be

determined by:

the analogue input signal

the analogue output components like DAC, preamp or power amp

the smallest word-size in the digital chain.

For digital systems to be transparent, dither is needed – this is described

on page 37. Whether the dither is added at the analogue–digital

conversion stage or later, it produces a defined noise-floor.

100

-20

10Hz

100Hz

10kHz

Frequency^1kHz

Figure 2. Showing audibility of noise in dithered channels of

different wordsize at very high listening levels.

In the diagram above, an audio system has been modelled for the loudest

reasonable listening circumstance – where peak levels reach 120dB spl.

The 'U'-shaped curve is the threshold of human hearing – sounds below

this are inaudible. The three curves show the human-audible-significance

of the dither level in 16, 18 and 20 bit channels. The diagram shows that

for a digital audio system to reproduce the whole scope of human hearing

without noise – 19 bits are needed.

For interest and comparison, the diagram below compares this

circumstance with LP records where the playback is set for 115dB

maximum.

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Figure 3. Showing the audibility of noise in the LP system for

comparison with digital channels.

Dynamic-range optimisation with Gain

The noise-floor of a digital system is determined absolutely by the lowest

preceding wordsize. For nearly all commercial material this is 16 bits.

518 allows you to get the best out of whatever comes next, by making

sure that the full output capability is used. Gain can be used in Resolution

Enhancement and Mastering to boost the level of the signal to fill the

available capacity.

For some reason, many CDs are recorded well below maximum level. By

boosting these we are able to reduce the audible effect of noise in

subsequent processing, or digital filters in DACs, or in the analogue

electronics.

Getting this right is easy – 518 immediately tells you if had to 'clip' the

output because you asked for too much. See page 18.

Dynamic-range optimisation with Pre-emphasis

Real-world music and speech signals do not have equal energy at all

frequencies. Typically the loudest sounds happen in the mid-range and

peak levels are much reduced above 5kHz.

This fact has been exploited extensively in audio systems over the years,

with a system known as pre-emphasis.

Input

Pre-emphasis

Channel

De-emphasis

Using Pre-emphasis and de-emphasis to improve channel performance

The diagram above shows the general pre-emphasis method. To take

best advantage of the channel – which could be an AM or FM radio link,

an LP record, a tape recording, a CD or a DAC – high-frequency signals

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are boosted. This boost process is called pre-emphasis. Now, in the

channel, the energy is more evenly distributed with frequency, and any

high-frequency noise and distortion in the channel is further below the

signal. In other words we get a better distortion and noise result in the

channel.

Before playing back the signal, we need to de-emphasise it to bring the

overall frequency response back to where it should have been. By cutting

the high-frequencies back, we also reduce the noise and distortion

introduced in the channel.

This process is used everyday for FM broadcast, tape and cassette

recording, for LP (RIAA pre- and de-emphasis) and for some CDs.

Now, boosting high frequencies is possible only when the program does

not have too much high-frequency content. Obviously anything that has

been through a pre- and de-emphasis process has the required spectrum.

The diagram below shows the pre-emphasis and de-emphasis curves for

CD – which are the curves used by 518. You can see that the highest

frequencies are boosted by nearly 10dB in the channel (on the disc).

Figure 4. Showing CD pre- and de-emphasis curves.

The 518 obtains resolution enhancement in making CD recordings by

using this pre-emphasis. All CD players know how to de-emphasise this

signal and recognise the pre-emphasis flag. When a signal coming in to

518 is pre-emphasised, the Emph light comes on. When 518 adds pre-

emphasis to a signal, the digital audio output stream carries an industry-

standard indication of pre-emphasis to tell downstream devices how to

handle this signal.

The 518 obtains resolution enhancement in playback systems by boosting

the high-frequency signals as it travels through signal processing or the

digital filters and conversion parts of a DAC. In the above diagram

'Channel' can be the digital and conversion part of an outboard converter.

The last block, 'De-emphasis' is normally in the final analogue sections of

the converter.

Well-designed converters use analogue de-emphasis so that all the noise

of the digital filters and converter are reduced. There are some cheap

implementations around that use digital-de-emphasis. This is bad design

and the benefits of this type of resolution enhancement are reduced if

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such converters are used. Meridian has always used correct analogue de-

emphasis in its designs.

By wrapping 72-bit precision pre-emphasis and analogue de-emphasis

around a DAC, it effectively gains:

one bit noise reduction

two-bit increase in high-frequency resolution

more than ten-fold (20dB) reduction of converter noise.

These are substantial gains and are clearly audible on a good system.

On some material, using pre-emphasis will raise the overall signal level to

give 'clip' messages. It is still a great step forward to use pre-emphasis

with some overall gain reduction. In other words, if using pre-emphasis on

a piece of music causes clipping, try using Emphasis with the gain

reduced to –2 or –3dB. You are still winning on resolution with most DACs

up to –6dB.

100

HP_Deem

-20

10Hz

100Hz

1kHz

10kHz

Figure 5. Showing the effect on audibility of the 518's High-

pass and Flat dithers. Also showing the noise reduction from

de-emphasis.

Dynamic-range optimisation with Noise-shaped

Dither

The section following page 37 describes some of the background to

noise-shaping.

Essentially noise-shaping works by an averaging method that is well

matched to human hearing. The noise-floor of the system is shaped by

moving energy from the mid-range – where listeners are most sensitive –

to high frequencies. A correctly designed noise-shaper allows the noise of

the channel to be made inaudible and allows resolution well below the

normal wordsize.

The diagram below shows how 518 can obtain inaudible noise and

effectively 20 bit resolution on a 16 bit CD!

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100

SBM

Shape C

Shape D

-20

10Hz

100Hz

1kHz

10kHz

Figure 6. Showing the effect on audibility of the 518's Shapes

C and D (C using pre-emphasis).

DAC enhancement by using high-frequency dither

The graphs above and in Appendix 1 (page 43) show that some of the

noise-shapers produce quite a lot of supersonic noise. This high level of

dither can have a very positive effect on DACs by causing them to

represent each level by averaging a large a number of different levels.

This high-frequency 'lubricant' tends to smooth out truncation and linearity

problems in real-world DACs.

Try the various shapes and see which one you like best in your system.

DAC or channel enhancement by word-length

matching

Digital systems work best if the input data is matched to the correct

wordsize for the device. Particularly where the signal has a larger

wordsize than the following device, then truncation distortion will arise.

The effects are real, but more subtle the other way round and are to do

with jitter and linearity.

In general 518 should be set to match the input and output wordlengths to

the incoming signal and following equipment. That will produce the

cleanest sound.

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Index

EPROM,version number, 18

Gain control, 19

500-Series, 5

562, 9

565

using with, 11

Help!, 41

Hiss, 41

Acknowledgements, 4

AES/EBU

digital audio connections, 29

Analogue sources, 9

Autoconfigure, 30

Input

changing for a source, 28

choosing in Config, 28

digital connections, 29

Inside 518, 7

Installation

Background noise, 41

Bypass, 33

customising, 13

general, 6

siting, 6

Types, 13

Introduction, 5

Cable

for digital audio, 29

CD improvement, 10

Clip

display, 18, 34

Communication

making connections, 30

Config

Jitter, 49

LaserDisc improvement, 10

Logo, 27

how to get into, 22

how to use, 24

overview, 21

Mastering, 31

examples, 34

hints, 46

how to use, 32

Memory, 14, 20

Menus, 19

Multimedia, 12

how to use, 32

Mute

Connections

AES/EBU, 29

Communications, 29, 30

digital, 29

digital audio, 29

general, 6

power, 29

Contents, 2

Customising

demuting, 19

how to, 19

how to, 22

making changes, 23

overview, 21

using Config, 24

using Type, 23

with Config, 21

with Type, 21

Noise shape plots, 43

Noise shapers, 36

Noise, audible background, 41

Normal

how to get back to, 23

Default settings, 21

Demute. see Mute

Digital

connection, 29

Display, 17

Operating

as preamp, 15

summary, 20

Output

digital audio connections, 29

Overview as preamp, 8

Overview as resolution enhancer, 10

Overview of mastering, 12

Overview of multimedia processor, 12

logos, 27

Dither explained, 37

DSP, 17, 33

DSP speaker improvement, 10

Dynamic range, 41, 50

Dynamic range explained, 38

Planning a setup, 7

Power switch, 14

Preamp

Emph light, 18

Emphasis explained, 38

Emphasis light, 18

overview, 8

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Index

Pre-emphasis explained, 38

Programming. see Customising

Surround sound, 11

Switching on, 14

Radio interference, 41

Recording, 34

Remote control, 18

Transfers, 35

Transparency explained, 37

Type

Repacking 518. see Unpacking

Resolution enhancement explained, 49

Resolution enhancer, 19

Restoring defaults, 21

RS232, 48

how to get into, 22

overview, 21

Unpacking 518, 6

Using

as control unit, 15

as mastering processor, 32

as resolution enhancer, 19

Service

where to get, 42

Setup. see Customising

automatic, 30

how to get into, 22

Specifications, 40

Standby

Version. see EPROM

Volume

display, 15

numbers, 15

Volume, adjusting, 15

display, 14

getting into, 18

to get out of, 18

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Notes

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Notes

518 User Guide

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