U S E R ’ S G U I D E
Stereo and Mono
Sidechain Compressor
plug-ins
For Tracktion 2
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Iconography
This icon will lead you to some further explanations of features and practical tips.
This icon marks information that is very important, so please make sure you have a
read.
This icon does not appear in this guide. Well except here of course.
Note: Visit our website at www.mackie.com to obtain the latest manuals and downloads
for all your Mackie products.
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Part No. SW0214 Rev. A 7/05
© 2005 LOUD Technologies Inc. All Rights Reserved.
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Stereo and Mono Sidechain Compressors for Tracktion
Contents
Mackie Software License-------------------------2 Examples -------------------------------------------21
Expansion--------------------------------------------21
Introduction ----------------------------------------6
Leveling ----------------------------------------------21
Main Features -------------------------------------- 6
Limiting ----------------------------------------------21
A brief word about Compressors--------------- 7
Hard Knee and Soft Knee Compression ------ 22
Snare Track Compression------------------------ 22
Standard vs. Sidechain Compressors ---------- 7
Specifications--------------------------------------23
Need Help?----------------------------------------- 23
Adding the Sidechain Compressor in
Tracktion --------------------------------------------8
Setting up a new Rack Filter--------------------- 8
Appendix: Using Compressors ---------------- 24
Dynamic Range------------------------------------24
What a Compressor does -----------------------24
Stereo or “Program” Compressors ------------ 25
Example 1: Compressor triggering from
another track -------------------------------------- 9
Setting up the Key Input ------------------------- 9
Setting up the Main Input----------------------- 10
Adding an EQ to the Key Input------------------ 11
Compressor Artifacts ---------------------------- 25
Breathing ------------------------------------------- 25
Pumping--------------------------------------------- 25
Example 2: Compressor triggering from
the same track ------------------------------------ 12
Setting up the Key Input to be the same as the
main input, but with an EQ ----------------------12
Working the Knobs-------------------------------26
The Compressor as a Tone Modifier----------- 26
Using the EQ to drop off the lows------------- 14
The Bottom Line ----------------------------------26
User Presets -------------------------------------- 27
Sidechain Compressor Features----------------15
Global Controls ----------------------------------- 16
The Contour Edit Screen ------------------------ 17
Threshold--------------------------------------------17
End Point---------------------------------------------17
Compression Ratio-------------------------------- 18
Gain Makeup and Auto Makeup --------------- 18
Attack and Release ------------------------------- 18
Soft Clip On and Threshold--------------------- 19
Node Editing --------------------------------------- 19
Node Selector Knob ------------------------------ 19
Reduction Meter----------------------------------20
Input and Output Meters -----------------------20
Input and Output OL LEDs ----------------------20
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Stereo and Mono Sidechain Compressors for Tracktion
Introduction
Thank you for choosing Mackie software prod-
ucts for your computer-based audio recording
system.
Main Features
•
Stereo and mono compressor plug-in for
Tracktion
The Stereo and Mono Sidechain Compressor
plug-ins come with Tracktion, our easy-to-use
music production software application. When
you install Tracktion, the plug-ins are automati-
cally installed in Tracktion's plug-ins folder.
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Key Input
Key Solo engage/disengage
Full stereo (or mono) operation
Rather fetching graphic display
Node edit selector
Note: These plug-ins only work with Tracktion,
and will not work with any other VST host ap-
plications you may have on your computer.
Global enable button
Favorite settings can be saved as presets
Memories A and B for quick comparisons
Input, output, and gain reduction metering
Release control
Typically, these plug-ins are used as compres-
sors, so that's why we call them that. However,
depending on the settings of the graphical in-
terface, they can act as compressors, limiters,
expanders, or a combination of all three.
Attack control
Threshold control
End point control
The Sidechain allows the compressor to take
its cue from a separate input, and apply its ac-
tion to another. For example, a vocal track can
drop the level of a music track (ducking), such
as when an announcement is made over back-
ground music, or where your vocals are a bit
lost in the mix.
Input level control
Output level control
Compression Ratio readout
Soft clip threshold control and indicator
Soft clip engage/disengage
Gain makeup control
The Sidechain Compressor can also take its
trigger input from a copy (or EQ'd copy) of it-
self. For example, it can be used as a basic
De-Esser, to compress the higher "Sssss"
sounds, or you can apply compression to a
guitar's mid or higher frequency range, leaving
the lower-frequency range uncompressed.
Auto gain makeup engage/disengage
Rugby ball inflator
The imaginary audio friend you always
wanted to come to life so everyone could
see that you were just not imagining things
The features of the Mono Sidechain Compres-
sor and the Stereo version are identical, so
this manual applies to both plug-ins. The
Mono version works for one key input and the
main input, and the Stereo version works its
magic for the key input and the stereo inputs,
stereo.wav, or after another stereo plug-in.
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Stereo and Mono Sidechain Compressors for Tracktion
A brief word about Compressors
Standard vs. Sidechain Compressors
As an example of how to use a
compressor, supposing you have a
track with a wide dynamic range.
This may have some exquisitely
detailed and quiet passages, played
before breaking into the final
crescendo of Heavy Metal final-
crecendo-ings.
A standard compressor detects the level of the
Loud
input signals from the main (host) track, and
applies the math to this track to produce the
processed output signals.
Wide
LEVEL DETECTOR
AND CONTROLS
Dynamic
Range
This track may overpower the oth-
er tracks during the loud passages,
and yet if we drop the track's over-
all level, the quiet passages may be lost in the
mix.
Quiet
INPUT
OUTPUT
A Sidechain compressor has an extra (Key)
input compared to a standard compressor. The
sidechain compressor can detect the level of
input signals from the main track OR the signal
level from an alternate source. The alternate
source can be a processed version of the main
track, or the output of a different track.
The compressor allows us to drop
Loud
(compress) the level of the higher
passages, once they get louder
Less
Dynamic
Range
than a threshold level. When
the music is quieter than the
threshold, it is not affected. This
decreases the dynamic range of the
track, and allows it to be a better
fit in the mix.
LEVEL DETECTOR
Quiet
AND CONTROLS
KEY INPUT
The overall level of the track can be adjusted
using the makeup gain, or automatic makeup
gain. This compensates for the reduced output
once the compressor has been at work, and lets
you place your track's level relative to the other
tracks.
INPUT
OUTPUT
The math or processing applied to the main
track reflects the signal fed into the sidechain.
In this way, we can have one track triggering
the compression of another.
The features and controls of this compressor
plug-in are similar to what you might find on a
real-life beer-stained electronic compressor.
If the key input signal goes above the threshold,
the plug-in will compute the amount of com-
pression and apply it to the main input (even if
it has not gone over the threshold).
If you add an EQ plug-in to the Key Input line,
you can narrow in on a desired frequency range
for your compressor to work from.
To make the connections in Tracktion, you must
use the Rack Filters option, and assign which
track will be connected to the Key Input. An
example of this is shown on the next page, so
fear not.
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Adding the Sidechain Compressor in Tracktion
The first thing to do is to open up Tracktion and
open your project.
Setting up a new Rack Filter
The Sidechain Compressors have an extra input
(the Key Input), and you must use the Rack
Filters feature of Tracktion to make this work.
This is really exciting and wonderful, so we
hope you will bear with us here.
Tracktion uses the term “filter” to refer to a
plug-in, be it native to Tracktion, or a 3rd party
plug-in such as a VST plug-in.
To add the plug-in to your tracks, simply drag
the icon labelled “new filter...” located just
above the filter section, and drop it where you
want the new filter to be placed. The figure be-
low shows a filter being added to track one.
Right-click on
the filter you
just added,
and select
"wrap this
filter in a new
rack filter"
from the drop
down menu.
The rack filter
section will appear, with the Sidechain Com-
pressor in place and its inputs, key input, midi,
and output lines shown connected.
Top Right of Tracktion Screen
Notice that the area in front of the volume/pan
filter is glowing red; this is how you can tell
where the filter will be placed. If there is no illu-
mination, then you are not currently over a valid
target area.
Once the “new filter” icon has
been dropped, a list of available
filters will appear, as if by mag-
ic. Choose the filter you wish to
add to the track from this list.
The Sidechain Compressors and
other plug-ins are available in
the "Mackie Plugins" folder of
this drop down menu.
The filter is now shown as a Stereo Sidechain
Comp Wrapper.
The next pages show some examples, with
steps showing how to set up the Key Input and
Main Input(s) to the Sidechain Compressor.
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Example 1: Compressor triggering from another track
Suppose you want to use the Sidechain Compressor as a "ducker," i.e., to reduce a music program
when you make an announcement. We can set up the Sidechain Compressor to take its Key Input
from a vocal track, and its main inputs from a music track.
Setting up the Key Input
1. Set up the Rack Filter on track 1 (for example), as shown on the previous page.
2. Click on the filter icon at the right of track 1, to bring up the rack filter details area.
–INF dB WET
0.0 dB DRY
3. In the rack filter details area, change the input destinations to be the Key Input. So now, the
sidechain compressor will get its Key Input from track 1.
4. If we were to play this track, there would be no output, because it is just feeding the Key Input. If
we set the Rack Filter to +0.0 dB DRY and -INF dB WET for track 1, then we will still be able to
hear its original form and beauty.
5. So here we are. Track 1 is set up to be the Key Input of the Sidechain Compressor, and yet it can
still be heard if you play it back. Its output is not affected by any Compressor settings.
Note: If you MUTE this track, it also mutes the Key Input.
continued..
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Setting up the Main Input
6. Add a new filter to track 5 (for example), but do not choose the
Sidechain Compressor. Instead, choose the Rack Filter you just set
up in step 1. Note: the Rack Filter is the same unit for both track
1 and track 5, and not two separate units.
7. Click on its icon, to bring up the rack filter details at the bottom of
the screen.
8. In the rack filter details area, set the input destinations of track 5 to be the left and right inputs
to the compressor (this is the default setting, but check it anyway).
9. Set these to be –INF dB DRY, +0.0 dB WET.
10.Click on the Sidechain Compressor drawing within the rack filter, to bring up the compressor
screen.
11. The settings you choose for the compressor will apply to track 5, but only when track 1 has
reached the threshold*. Your track 1 vocals can duck the track 5 music by an amount depending
on your compressor settings. (You can also use this method to make your vocals a bit more dis-
tinct from a track with more dynamics.)
*Note: Gain Makeup and Auto Gain will still affect your music track, even when no compression
is taking place (no vocals or other key input present above the threshold), so make sure you ini-
tially adjust them to prevent overloading your music track. Perhaps set the Auto Gain off, and the
Makeup Gain to 0 dB to start.
12.To listen to track 1 vocals, press the Key Solo button.
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Adding an EQ to the Key Input (an optional and fun thing to do)
13. Add a new filter inside the rack filter (instead of to the right of the tracks), and choose an EQ.
14.Then click on the Key Input connecting line and use the mouse
to hook the EQ in-line. Use the EQ graph to adjust its parameters
to suit your delicate audio sensibilities. Select the Key Solo but-
ton to audition the Key Input.
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Example 2: Compressor triggering from the same track
Tracktion's wonderful rack filter system lets you make the key input the same as your main input.
One application for this, is to make a De-Esser to get rid of high "Ssss" sounds on vocal tracks.
Dedicated De-Essers have more fine features and controls, but this will give you a basic functioning
model.
Setting up the Key Input to be the same as the main input, but with an EQ
1. Set up the rack filter on track 1 (for example), as shown on page 8.
2. Drop a new filter inside the rack filter (instead of to the right of the track), and choose an EQ.
3. Inside the rack filter, hook up the left and right inputs, to the left
and right inputs of the EQ.
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4. Connect the left and right outputs of the EQ to the Key Input of the compressor.
5. Adjust the EQ to boost the higher frequencies where the "S" sounds lurk. A bit like this (although
this is a more extreme example):
6. And now, here we are. The Key Input is a copy of the main vocal, only with the EQ section actu-
ally boosting the S frequencies we don't want. Hmmm... that might seem a bit odd, but there is a
method to the madness.
The Key Input (boosted S sounds) trigger the compression when the S sounds cross the thresh-
old. This compression occurs to your main vocals, and eliminates the nasties.
Experiment with the EQ settings and the compressor settings to hone-in on audio loveliness. You
don't want the EQ to be triggering compression for frequencies you want to keep.
Remember that the Compressor's Key Solo button is your friend. It will let you listen to the
(EQ'd) Key Input, as you find the frequency range you want to ultimately compress.
Key Solo
7. Here is a rough guide to setting up the compressor controls as a De-Esser. (The controls are de-
scribed in more detail in the rest of the manual.)
Use:
Short Attack time and short Release time.
Compression Ratio around 2:1 or 3:1.
Gain reduction of no more than 3 to 6 dB, otherwise the singer might sound like they have a lisp
(well, unless you want that, or it is an improvement).
Soft Knee sounds more natural, so add a few compressor nodes to gently bring in the compression.
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Using the EQ to drop off the lows
There is another useful and common application for a Sidechain Compressor:
If you have a Guitar track, and you do not want the low frequencies compressed, you can place an
EQ in the Key Input to roll off the lows. The EQ passes only the mids and highs into the Key Input,
and therefore the compressor will only apply compression for these frequencies. It will not compress
during the dynamic low-frequency manglings your guitarist is known for.
1. Follow steps 1 to 4 on pages 12 and 13 to add the Sidechain Compressor to your guitar track.
2. Click on the EQ to bring up the EQ graph, and adjust it to roll off the lows. Use the Key Solo but-
ton on the compressor to audition its effect.
3. Remember that the rolling-off is only happening to the Key Input, and not your main guitar track.
It just means the compression will not be triggered by any low-frequency peaks.
4. You can use this technique to make the compression occur (or not occur) for any frequency band
you wish.
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Sidechain Compressor Features
Global Controls
Contour Edit Screen
Compressor Controls
The Main Screen is made up of two sections:
•
•
Global Controls
Compressor Controls and Contour Edit
Screen
The Global Controls section includes the Lock
and Hide buttons, Preset up/down buttons, Pre-
set title window, Active, Menu, and Mem A/B
buttons.
The Compressor Controls section includes most
of the controls and readouts. You can use your
mouse to move the sliders left or right, or to se-
lect nodes with the Node Selector knob.
The Key Solo button allows you to listen to the
key input on its own.
The Contour Edit Screen shows a graphi-
cal interface of the compressor contour, and
meters showing input and output levels and
gain reduction. The compressor contour can
be changed by grabbing the nodes and moving
them around.
These sections are described in the next few
pages.
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Global Controls
Lock
Save User Preset As...: Saves a Preset to the
If this is pressed, the compressor's interface
will not disappear when you select other items
or areas in Tracktion.
hard drive with a new file name. (For example,
use this after making slight changes to a preset,
and saving it as a variation)
Save User Preset: Saves changes to the current
preset to the hard drive.
Hide
This hides the compressor interface from view,
and is useful if you have previously selected
"Lock."
Reset Comp: Resets all the settings to the cur-
rent preset values.
Cut Comp: Copies all the settings to the clip-
board and resets them to their default values.
Copy: Copies all the settings to the clipboard,
leaving the settings as they are.
Preset Toggle Buttons
You can save your own favorite settings as pre-
sets for later recall.
Paste Comp: Copies the settings from the clip-
board to the current window.
The up/down arrow buttons on either side of the
preset window enable you to scroll up or down
through the user presets.
Note: Cut/Copy/Paste are useful for changing
Mem A and B to identical settings.
Memory A/Memory B
Preset Title Window
The Mem A and Mem B buttons temporarily
store all the current settings of the compressor
to allow comparative referencing. You can also
copy and paste settings from one memory loca-
tion to another using commands found on the
menu.
This window displays the currently selected
preset. Click on it to access the pull-down menu
where you can choose your previously-saved
user presets.
If you have loaded a preset, and then moved
one of the controls, an asterisk will appear next
to its name, as a reminder that things have
changed. If it sounds good, save it as a new pre-
set for later recall. If it doesn't sound good, you
can always create the ultimate "Sucks" preset.
Active
Use this to engage or disengage the compres-
sor from the signal path. If the red LED is on,
the compressor is active, and any audio passing
through is affected by its settings. If the red
light is out, then the compressor is bypassed,
and it has no effect on the audio.
Menu
Pressing the MENU button opens a pull-down
menu that performs some familiar functions:
About Stereo Comp: Opens a window that shows
the version number and copyright information.
Undo: Undo the previous action.
Redo: Redo the previous undo.
Load Comp: Loads a previously saved preset
file.
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Threshold
The Contour Edit Screen
The level at which the compressor starts work-
ing is called the threshold. The compressor will
reduce the level of signals above the threshold
volume level and not affect lower-level signals.
0
-6
You can adjust the threshold by grabbing the T
node on the graph, or by adjusting the slider.
-12
-18
-24
-30
-36
-42
-48
The threshold has been set here to –30 dB, so
any input levels lower than –30 dB are not af-
fected by the compressor. For example, an input
signal of –42 dB has an output of –42 dB, (as-
suming no Makeup gain has been added).
End Point
-48 -42 -36 -30 -24 -18 -12 -6
INPUT LEVEL dB
0
You can adjust the End Point by grabbing the E
node on the graph, or by adjusting the slider.
The End Point shown here, is set to an output
level of –18 dB.
This interactive graph does not show the ac-
tual input or output signals dancing across the
screen. It shows the contour we can apply to
the compressor to make it work as we want it
to. It's a bit like a Jello mold, it's shape affects
the shape of the Jello.
Any input signals higher than the threshold will
be attenuated by an amount determined by the
slope of the graph. For example, if the input
level is –12 dB, follow the –12 dB line vertically
until it hits the line joining the T and E nodes.
From there, follow horizontally to the left, and
read the output level (approx –23 dB).
The input signal level in dB is the horizontal
axis, and the output level is the vertical axis,
with 0 dBfs at the top, and –48 dBfs at the bot-
tom (dBfs = dB full scale).
If the compressor did nothing to your signal,
then the contour curve would just be a straight
diagonal line, going from bottom left to top right
(input=output).
As a test, sit up straight, get a 2B pencil and fill
in the output levels for the following input lev-
els, from the graph:
The example above shows a simple set up, with
just the Threshold (T) and End Point (E) in
place. Further nodes can be added between the
threshold and end point, to really make things
fly. See the Node Editing section on page 19.
Input Level dB
Output Level dB
0
–6
–12
–18
–23
OK, sorry about the test there.
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When AUTO MAKEUP is IN, the compressor au-
Compression Ratio
tomatically chooses an appropriate makeup gain
for you. This is based on your dynamics contour.
You can still use the ‘manual’ gain makeup con-
trol in this case. It merely adds to the makeup
gain automatically applied. When you first set the
AUTO MAKEUP to IN, the compressor adjusts
your makeup gain parameter so that the volume
does not suddenly jump up. This is hearing (and
speaker) protection!
The compression ratio compares the change
in input level with the change in output level.
From the graph on the previous page, the input
range from 0 dB to the threshold is –30 dB.
From the graph, this input range is compressed
into an output range of –12 dB, and the ratio is
30/12 (= 2.5/1).
Attack and Release
Attack specifies how quickly gain reduction (or
expansion) occurs at the attack, or beginning,
of a signal crossing the threshold.
If we select the E node, the ratio in our example
is displayed as 2.50:1. (For signals above the
threshold, a 2.5 dB change in input level will
yield 1 dB change in the output level.)
Release controls how quickly gain reduction
backs off when the signal drops back down. The
time is measured in milliseconds, and corre-
sponds to the length of time it takes to achieve
a fixed amount of compression (or expansion).
The displayed ratio is the ratio of the line seg-
ment to the left of the selected node.
Negative compression ratios can also be shown.
This is useful mainly for special effects or re-
pair work. In this case, a node appears lower
in the graph than the one to its immediate left
so its line segment is going downwards. For
negative compression, the ratio is negative, for
example, –2.5:1.
In general, the attack time should be much
faster than the release time to get pleasing re-
sults. If the attack time is set too quickly, you
hear something resembling clipping on attacks,
especially with low-frequency signals. Leaving
the attack a little bit longer also allows more
of the ‘snap’ of the attacks to pass through the
compressor. Setting a release time too fast can
result in ‘buzzing’, especially on low notes. This
occurs because the compressor gain is actu-
ally following individual cycles of the incoming
waveform.
The ratio can display compression or expansion.
When a line segment represents expansion, the
ratio is displayed as, for example, 1:2.5. (See
the page 21 for more about expansion.)
Gain Makeup and Auto Makeup
Gain Makeup is used to make up for volume
that has been decreased due to compression.
The Gain Makeup level ranges from –15 dB of
attenuation, to +15 dB of gain, and can be ad-
justed by moving the slider to the left or right .
If you set the attack time to 0 ms, the dynam-
ics section will compress everything over the
threshold, allowing no transients through un-
processed. The amount of compression depends
on the ratio.
Generally, lower frequencies require longer
release times than higher frequencies. For high-
or mid-frequencies, if the release time is too
long, you may hear the compressor ‘breathing’.
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Soft Clip On and Threshold
The Soft Clip switch activates a soft-clip limiter
circuit. There is also a threshold slider. When
the output level goes above this threshold, the
soft-clip circuit kicks in. This circuit starts add-
ing analog-style distortion, which rounds off
transient peaks, and avoids the harsher sound
of a straight digital clip. The lower the thresh-
old, the more analog-style distortion is added. If
the threshold is set too low, you hear this as a
very crunchy distortion sound. It is best to keep
the threshold between –3 dB and –1 dB unless
you are going for a special sound effect.
Nodes can be added to the contour graph by
right-clicking the mouse on the contour graph.
Right-clicking on the graph where there is no
node adds a node, up to a maximum of 4. Right-
clicking on an existing node removes it.
The Soft Clip LED (next to the slider) activates
when the signal is above the soft-clip threshold,
so keep an eye on it.
The four numbered nodes always appear in
order from left to right. You can't add a node be-
tween, for example, nodes 1 and 2, even if they
are the only nodes active.
The soft-clip circuit is the last thing in the sig-
nal processing chain.
Node Editing
Node Selector Knob
So far, we have just shown the use of the
threshold and end point controls to set up a
simple compressor.
One of the very powerful features of the com-
pressor, is it allows you to draw your own curve
between the threshold and the end point, and
really shape that Jello mold. Up to four nodes
can be added to the curve. This depth of editing
is helpful in defining detailed nuances in your
curve such as hard knee, soft knee, and expan-
sion.
You can also add or remove nodes by using the
Node Edit Selector knob and toggling the Active
Node switch. Click on the knob and move the
mouse either vertical or horizontal to rotate it
and select a node. Use the Active Node switch
to turn a node on or off.
The figure below shows 3 extra nodes – labeled
1, 2, and 3. These nodes are being used, in
this case, to essentially draw a knee for the
compressor curve. This gives a nice smooth
transition from applying minimal compression
at low input levels, to much higher compression
at higher levels.
The position of a selected node can be adjusted
by using the Input and Output level sliders.
These sliders do not appear for the threshold
and End Point nodes, just nodes 1 to 4.
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Reduction Meter
Input and Output OL LEDs
The small boxes at the right of the input and
output meters are the overload LEDs. They
light if the signal goes above 0 dB, and this
should be avoided. Most little red lights which
come on should be avoided, like that one in the
car which says "Oil."
You can generally get rid of clipping by backing
off the makeup gain slider slightly, or by engag-
ing the Soft Clip switch (see the previous page).
The reduction meter along the right edge of the
screen shows the overall reduction in output
level due to the compressor operation. If you
are using expansion, then there will be an in-
crease in output level. This meter will help you
add or adjust the makeup gain.
The meter reads 0 dB whenever the input is
below threshold, and moves down as the input
level goes above threshold and gain reduction
starts.
Input and Output Meters
The meters below the graph show the input lev-
els of the signals going into the compressor and
the left and right output levels.
The stereo compressor takes its input from a
mixed sample of the left and right, so there is
only one input meter. Its compressor action
then works equally on the left and right of your
stereo track.
It is interesting to see the position of the
threshold with respect to the input level meter,
and to see the output meters. Some say they are
almost hypnotic, and you can even predict Lotto
numbers.
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Leveling
Examples
Having expansion for low input signals, and
compression for higher signals is a good way to
level out a signal's dynamics. Quiet signals be-
Expansion
The red diagonal line added to the graph below,
represents unity gain (i.e., the output signal is
the same level as the input signal). Contours
which are steeper than this, like the segment
between T and node 1, represent expansion,
those not as steep, compression.
come louder, and louder signals become quieter.
We see an example of this below. For input sig-
nals below node 2 in amplitude (approximately
–28 dB), the dynamics processor acts as an ex-
pander. For signals above node 2, the processor
is a compressor.
Limiting
When you just want to limit the signal to not go
beyond a certain level, set the end point to be
the same level as the threshold (Ratio =
infinity:1), and keep the Attack time low.
Expansion occurs when the output level change
is more than the input level change. For exam-
ple, a 3 dB change in input level, might give a
4 dB change in output level.
Compression occurs when the output level
change is less than the input level change. For
example, a 3 dB change in input level, might
give a 2 dB change in output level.
Deft use of the nodes allows expansion or com-
pression above the threshold. Expansion can be
used to increase the volume of quiet passages,
and bring a little bit more "life" into a perfor-
mance. Note that each individual segment can
be set as either a compressor, or an expander.
Just look at the slope between each node. If it
is steeper than the diagonal, this is expansion,
and if not so steep, compression.
Note that in the above example, the reduction
meter and the output level meters are showing
an increase (expansion) in level.
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Hard Knee and Soft Knee Compression
Snare Track Compression
The terms hard and soft do not refer to sound,
but rather the way that the compressor reacts
to incoming signals. The difference is somewhat
subtle to hear, but is more apparent at higher
compression ratios. A hard knee setting is well
suited to lower ratios. When using higher com-
pression ratios, you may find it a little better-
sounding to draw in a smoother knee curve.
The graph below could be used on a snare track
to drastically lower the volume of a few snare
hits by an over-excited drummer, while leaving
most of the snare track unaffected.
A hard knee curve is represented as a straight
line that connects a point on the threshold to
the end point or maximum output on the graph.
A soft knee curve has a smoother curve that
connects the two points. This creates a more
gradual transition between non-compressed and
compressed signals.
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Specifications
Dynamics
Gain Makeup
± 15 dB
Attack
0 to 100 ms
Release
30 ms to 3000 ms
–48 dBfs to 0 dBfs
Threshold
Compressor Contours
Four nodes per each allowing for any possible compression or
expansion ratio from 1:inf to inf:1
Input/ Output Meters
–48 dBfs to 0 dBfs
Reduction Meter
+ 12 dB to -12 dB
Soft-Clip
Threshold
0.0 dB to –20.0 dB
Weight
Stellar Astrophysics shows us this is about the same quantum
weight as a small Wildebeest who has been working out. A
lot.
Dimensions
It depends if the Compression Ratio is set to "12 acres" or
"half a meadow."
Directions
Butter both sides, add a slice of sharp cheese and enjoy with
your favorite track.
Please Note
During the hamster chariot-racing scene in this manual, no
hamsters were hurt, miffed a tad, or even ticked-off slightly.
Need Help?
Contact our Technical Support staff at 1-800-898-3211, Monday to Friday,
from 7 am to 5 pm PST. After hours, please visit www.mackie.com and look
under Support, or email us at techmail@mackie.com.
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theoretical – a 24-bit system is theoretically ca-
Appendix: Using Compressors
Compression has become such an integral part
of mixing, that we thought an appendix might
be called for.
pable of 144 dB of dynamic range but practical
things like electronic components stand in the
way of actually achieving it in practice, at least
today.
Even in the best of control rooms, we have to
squeeze as much as 115 dB of obtainable dy-
namic range into a 95 dB box. For the rest of
the world, though, we have to squeeze harder so
soft passages don’t get lost when your neighbor
starts up his lawnmower, or when listening to
the car radio at 65 miles per hour with the top
down. Therefore we can’t record all the dynamic
range that’s available if we expect people to
hear all the music we record.
Dynamic Range
To use a compressor effectively, it’s important
to understand the concept of dynamic range.
Dynamic range is the difference between the
loudest and quietest signal levels passing
through the system chain. The span between
"barely audible" and "physical discomfort" is
about 120 dB, so we consider this to be the dy-
namic range of human hearing. Anything below
the threshold of hearing will be lost, as will
anything above the threshold of pain. But how
much dynamic range do we need in our record-
ings, or, more importantly, how much can we
really use?
What a Compressor does
A compressor reduces dynamic range. When
used properly, it’s hard to detect the action of a
good compressor, but a compressor can also be
used creatively as a sound shaping tool. A com-
pressor can be inserted into a single channel in
the recording chain when recording or mixing a
track, or compression can be applied to an en-
tire mix or sub-mix.
Few people listen in a totally soundproofed
room. A very well-designed studio control room
has an ambient noise level 10 to 15 dB above
the threshold of hearing. Since we want to
keep ourselves safe from hearing damage, 95
dB or so is about all the dynamic range we can
use. But consider this: A very quiet living room
has an ambient noise level 25-30 dB above the
threshold of hearing. The inside of an automo-
bile at reasonable driving speed is upwards of
60 dB above the threshold of hearing, and with
a window open, all bets are off.
Let’s look at applying compression to a vocal
track. Hard consonants such as the letter ‘T’
create a high initial sound level before settling
down, whereas most vowels tend to be more
even. The average volume level of a word may
be fairly low, but because of an initial loud con-
sonant, we can only raise the word’s volume so
far before running out of headroom. If there’s
music playing under the voice, even when boost-
ing the vocal level as high as possible without
distorting the attack, a word (or a syllable) may
be far enough below the level of the music to
become lost or misunderstood.
Average consumer audio systems aren’t capable
of producing painful sound pressure levels (with
the exception of those cars that cruise by with
the bass pumping loud enough to rattle the
windows in your house), a typical listening en-
vironment can only support a dynamic range of
65 to 75 dB.
If we reduce the gain momentarily during the
loud attack, then bring it back up when the dis-
tortion-risking blast is over, we can now boost
the average level of the word so that it can be
understood clearly over the music. What we’re
doing here is reducing the dynamic range of the
word, the difference between the loudest and
softest parts. By doing that, plus boosting the
The electronics in our recording chain are much
better than that, with digital recorders and ana-
log or digital consoles capable of 105 to 115 dB
of dynamic range. This means that the listening
environment, not the gear, sets the practical
limit on dynamic range. If you see a number
greater than that on a spec sheet, it’s purely
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level, we’ve made the vocal track louder in the
Compressor Artifacts
Two uncomplimentary terms often used to de-
scribe the sound of a compressor are breathing
and pumping.
mix without reaching a volume at any point that
will cause distortion. To do this requires a very
fast compressor or limiter, but it’s a good ex-
ample of the principle.
Since to most listeners, louder equals better,
another use for compression is to make a mix
sound louder. Often there’s a single sound - a
snare drum for example – that’s noticeably loud-
er than anything else in the mix. A drummer
hits the snare louder on some beats, and the
loudest hit determines the maximum level that
can be recorded. By compressing the overall
mix and sitting on the loudest hits, the average
level of the song can be raised.
Breathing
Breathing is most noticeable on a solo voice
and is often, in fact, the sound of the vocalist
breathing. If release time is short, the gain rises
quickly during pauses between words, just as
the singer takes a breath. The increased gain
makes the breath more audible.
Hearing a singer taking a breath may not al-
ways be desirable or dignified, but at least it’s
organic. Few recordings are made in an abso-
lutely silent environment, however. Any ambient
noise in the room will be boosted when the gain
rises, creating an artificial “breathing” sound,
perhaps even bringing leakage from the singer’s
headphones along with it.
Stereo or “Program” Compressors
A compressor is basically a single channel
device, but stereo compressors, often called
“program compressors,” are most often used to
compress a full stereo mix.
All compressors exhibit some breathing, but
careful adjustment (which includes controlling
room acoustics and mic positioning) can mini-
mize it.
The thing that differentiates a stereo compres-
sor from simply patching one compressor into
each channel is that the signal that controls
the amount of gain reduction is shared by both
channels.
Pumping
Pumping is another compressor artifact. It’s
more apparent when compressing an overall
mix than a single track.
Reducing the level of one channel of a stereo
pair will cause the balance to shift to the louder
side. We don’t want the stereo image to wander
around when one channel goes over threshold
and the other one doesn’t, so we connect the
level detectors of the two compressors together.
Now when either channel requires some gain
reduction, that same amount of gain reduction
is applied to both channels.
One instrument in the mix that’s louder than the
others will trigger the compressor into action.
If that instrument stops playing, even for an
instant, the level of the mix will increase notice-
ably. Each time the dominant instrument starts
or stops, it “pumps” the average level of the mix
up and down.
Compressors that work best on full program
material generally have very smooth attack and
release curves and a slow release time to mini-
mize the pumping effect.
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compressed, often allowing you to increase the
impact of the kick drum without increasing the
level of the track in the mix.
Working the Knobs
Lowering the threshold while keeping the
compression ratio fixed reduces the maximum
output level, since you’re compressing over a
larger portion of the dynamic range of the in-
put signal. By keeping the threshold fixed but
increasing the compression ratio, you’ll reduce
the output level by compressing only the loud-
est signals. There are no rules for this. Let your
ears be your guide, with the meters as a sanity
check.
Compressors with very fast attack time that of-
ten work well on vocals, work poorly on a bass
because the compressor actually tries to follow
the individual cycles of the waveform rather
than the envelope of the note. This characteris-
tic can be used as a special effect, but usually it
just takes all the life out of a bassy instrument.
Some people put a hardware compressor in-
line with a signal, with the controls set for no
compression action at all. One reason is that
they like what the electronics of the input and
output amplifiers do to the sound. This is most
noticeable with “vintage” units that use tube
electronics – a mighty expensive tube-in-a-box,
but if it’s there and it works, there’s no reason
not to use it.
As an exercise, try plotting out a few combina-
tions yourself. Then set up your compressor and
listen to the differences.
The Compressor as a Tone Modifier
Adjusting the attack and release times of a com-
pressor applied to an instrument can change
its timbre by rounding off a sharp attack or
stretching out the sustain portion of the note’s
envelope. It’s sort of like having an equalizer
with a different parameter.
The Bottom Line
A compressor can never be used by the book
– not even this one. You need to listen carefully
when you make adjustments. By understanding
the effect of each of the adjustable parameters,
you’ll be better able to reach your goal quickly.
A drum hit can be “stretched out” by applying
a long release time, a healthy gain boost, and
fairly high compression ratio.
Compressing low-frequency program material
requires special care. The attack and decay por-
tions of a kick drum are 60 to 80 milliseconds
long, but a low-pitched kick has a fundamental
frequency of about 40 Hz. This means that only
three of four cycles of the kick’s fundamental
frequency are heard on each hit, much of that
being in the decay portion of the envelope.
Compressing the drum with a fast attack time
and high compression ratio will make more
cycles of the attack portion of the drum audible,
making its “thump” sound much more pro-
nounced without having to boost low frequency
gain with an equalizer. Try this next time you
want a kick in the chest.
The beater attack is at a higher frequency
(1 to 3 kHz) so a moderately fast attack will let
a few cycles of beater through while working
on the low “whump.” Slowing down the attack
lets more of the beater sound pass before being
Answers
D . S u s i e h a d t h r e e m o r
C . E a c h a l t e r n a t e W
B . T h e R e d S o x b y t h r e
A : B a l t i m o r e
e d n e s d a y
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