Copyright: Copyright © Twelve Tone Systems, Inc.


Contents
Cakewalk FX Pack 1: Dynamics Processor

An introduction to dynamics processing

Compressor/Gate

Limiter

Expander/Gate

Dynamics Processor

Stereo handling

The interactive graph

Glossary


An introduction to dynamics processing

Dynamics processors are a class of audio effects that modify the dynamic range of an audio signal. The dynamic range of an audio signal is a measure of the level of variation between the loudest and softest parts of the signal. The volume, or level, of a digital audio signal is normally measured in units of decibels, or dB. When working with 16-bit digital audio, the range of values for signal level ranges from approximately -96dB (silent) to 0dB (maximum volume).  The decibel scale is logarithmic -- each increase of 6dB (say, from –96dB to –90dB, or from –36dB to –30dB) represents a doubling of the signal level.

There are several different types of dynamics processors.  A compressor takes the loudest parts of an input signal and reduces their volume.  A compressor only affects those portions of the signal that are louder than a certain level, known as the threshold.  Portions of the signal that exceed the threshold are reduced toward the threshold by a set factor, known as the ratio.  Most compressors also raise the level of the entire audio signal by a certain amount.  This amount is known as the master gain.  Both the threshold and the master gain are measured in decibels.  The compression of the loudest parts of the audio signal helps to make sure that the average signal level can be boosted without exceeding the maximum allowable peak level.  In general, the master gain should not exceed the reduction in dynamic range that results from the compression.  If it is larger, clipping may result.  Compressors are usually applied with compression ratios ranging from 1.5:1 to 8:1.  An as example, suppose that a compressor is set with a threshold of –18dB and a ratio of 3:1.  In input signal of –12dB (6dB above the threshold level) will produce an output signal of –16dB (only 2dB above the threshold).  The amount by which the signal exceeds the threshold is reduced by a factor of 3.   When the ratio is much higher (around 10:1 or more), a compressor effectively prevents the audio signal from exceeding the threshold value.  In this case, the effect is referred to as a limiter.

An expander takes the softest parts of an input signal and reduces their volume.  An expander only affects those portions of the signal that are softer than a certain level, once again known as the threshold.  Portions of the signal that fall below the threshold are reduced below the threshold by a set factor, known as the ratio.  When the ratio is high, an expander effectively eliminates all portions of the audio signal that fall below the threshold.  In the extreme case, this is known as a noise gate, or simply a gate.

When a signal exceeds the threshold level of a compressor, or falls below the threshold level of an expander, the signal is modified.  The attack time is the length of time it takes the dynamics processor to respond to increases in signal level.  The release time is the length of time it takes the dynamics processor to respond to decreases in signal level.  In general, attack times are set to be relatively short, while release times are much longer.  This means that compressors and limiters generally activate quickly and release gradually, while noise gates close slowly, and then re-open quickly.  By adjusting the attack and release times, you can produce smoother changes in signal levels that might otherwise change abruptly.   If the attack time is too short, you may experience unnatural or sudden changes in volume.  If the attack time is too long, the dynamics processor may not have the effect you want.  If the release time is too long, compression may continue through low-volume sections of audio, making them inaudible.

All dynamics processors monitor the input signal to estimate the current signal level.  The estimate is made using one of several common level detection methods:

Level detection method	When it is useful
Peak	Most useful for limiting
Average	Most useful for instrumental solos
RMS	Most useful for vocals and speech

See Also:

Compressor/Gate

Limiter

Expander/Gate

Dynamics processor

Interactive graph

Stereo handling


Compressor/Gate

A compressor takes the loudest parts of an input signal and reduces their volume.  This effect includes the following parameters.

Setting	Range of values
Compressor Threshold	From the gate threshold to 0dB
Compressor Ratio	From 0:1 to infinity:1
Gate Threshold	From –108dB to the compressor threshold
Gate Ratio	From 0:1 to infinity:1
Attack Time	From 0.1ms to 20ms
Release Time	From 50ms to 3000ms
Master Gain	From –24dB to +24dB
Level Detection Method	Peak, average, or RMS
Stereo Handling	Maximum or Side Chain
Envelope Curve	Soft knee or hard knee
When to Use a Compressor/Gate

There are a variety of reasons why you might want to use a compressor:

•	Compressors enable you to increase the overall signal level of a mix, without causing the distortion that would result from exceeding the maximum allowable peak level.   Increasing the average signal level makes a recording sound louder, with an apparent increase in “punch.”

•	If you plan to reproduce your audio using a medium with limited dynamic range, such as magnetic tape, the increase in the average signal level that you achieve with a compressor helps prevent important audio material from being lost in the background noise.

•	Compression can even out unwanted volume changes to achieve a smoother and fuller sound.  For example, if a vocalist moves closer in and further away from a microphone while making a recording, the recorded volume levels may be uneven.  A compressor can smooth out theses variations.

•	During mixdown, you can use a compressor to adjust the dynamic range of individual tracks. This is one way to balance the tracks, and can even reduce the need to use a lot of equalization.

•	Compressors can be used to increase an instrument’s sustain, by using a release time longer than the instruments decay.

•	With extreme compressor settings, you can produce new interesting sounds from familiar sounds.

When you use a compressor, the master gain adjustment can result in increased low-level system noise.  As a result, it is common to use a gate in combination with a compressor.   A compressor/Gate combines a compressor and a gate into a single effect, so you can increase the overall dynamic level of an audio signal, without distorting the loud parts, and without excessively boosting low-level noise.   The gate threshold is normally set low enough to remove low-level system noise, but not high enough to remove important program material.

Since other audio effects can produce background noise, you normally place the noise gate near the end of the effects chain.  However, if you’re using delay and reverb effects, you may want to place them after the noise gate, so that the sound trails off naturally rather than being truncated suddenly by the gate.

Here are several common problems you can run into when using a compressor:

Problem	Explanation
Breathing	If the audio material has a wide dynamic range, the output gain of a compressor can vary greatly. The greatest change occurs immediately after the input signal crosses the threshold.  If the input signal fluctuates around the threshold, then the output level will increase and decrease repeatedly.  The resulting rise and fall of low-level background noise can result in an annoying “breathing” effect.  To prevent this effect, use a lower compression ratio, or increase the release time.
Pumping	Pumping can occur when you compress a mix where one instrument is louder than all others.  Whenever the loudest instrument is silent, even for a brief moment, the overall level of the other instruments will increase dramatically.  As the dominant instrument comes in and out of the mix, the compressor will increase and then reduce the level of the other instruments. This results in an undesirable “pumping” effect.  To prevent this effect, decrease the level and/or dynamic range of the dominant instrument in the mix, increase the threshold, or use a lower compression ratio.
Noise	Set the gate so that the noise floor is not boosted significantly during quiet passages.
Harmonic Distortion	If the release time is too short when compressing or limiting low-frequency signals (such as a bass guitar), the compressor or limiter can respond to the actual individual cycles of the waveform, causing harmonic distortion.  To prevent this effect, increase the release time.
Preset

Use this field to choose and enter presets.

Audition

Click on this to hear the results of the command on the first three seconds of the selected audio.

See Also:

Limiter

Expander/Gate

Dynamics processor

Interactive graph

Stereo handling

An introduction to dynamics processing


Limiter

The purpose of the limiter is to prevent the audio signal from exceeding a threshold value.  A limitter may be seen as an extreme case of compressing  Its parameters include

Setting	Range of values
Compressor Threshold	From –40dB to 0dB
Master Gain	From –24dB to +24dB
Stereo Handling	Maximum or Side Chain

The most common problem caused by the use of a limiter is excessive distortion.  This indicates that the limiter is active too much of the time, or that the master gain is set too high.  To correct the distortion, lower the master gain or increase the threshold.

Preset

Use this field to choose and enter presets.

Audition

Click on this to hear the results of the command on the first three seconds of the selected audio.

See Also:

Compressor/Gate

Expander/Gate

Dynamics processor

Interactive graph

Stereo handling

An introduction to dynamics processing


Expander/Gate

The stereo expander expands the dynamic range of the portion of an audio signal which falls below a given threshold.  If you use the graph to control the settings, note that the graph shows only two visible nodes, allowing only the initial slope representing the expander to be moved.  Its parameters are listed below.

Setting	Range of values
Expander Threshold	From –108dB to 0dB
Expander Ratio	From 1:0 to 1:infinity
Attack Time	From 0.1ms to 200ms
Release Time	From 20ms to 1000ms
Master Gain	From –24dB to +24dB
Level Detection Method	Peak, average, or RMS
Stereo Handling	Maximum or Side Chain
Envelope Curve	Soft knee or hard knee

Here are several common problems you can run into when using an expander:

Problem	What to do
The beginning of a sound is cut off	Decrease the attack time
The end of a sound is cut off	Increase the release time
Disturbing sudden change in background noise as the expander cuts in and out	Lower the expansion ratio or increase the release time
Preset

Use this field to choose and enter presets.

Audition

Click on this to hear the results of the command on the first three seconds of the selected audio.

See Also:

Compressor/Gate

Limiter

Dynamics processor

Interactive graph

Stereo handling

An introduction to dynamics processing


Dynamics processor

The stereo dynamics processor plug-in combines the functions of all the other dynamics processors in a single unit. If you use the graph to control the settings, note that a maximum of four nodes are allowed in the graph.

Setting	Range of values
Compressor Threshold	From the expander threshold to 0dB
Compressor Ratio	From 0:1 to infinity:1
Expander Threshold	From –108dB to the compressor threshold
Expander Ratio	From 1:0 to 1:infinity
Attack Time	From 0.1ms to 200ms
Release Time	From 20ms to 1000ms
Master Gain	From –24dB to +24dB
Level Detection Method	Peak, average, or RMS
Stereo Handling	Maximum or Side Chain
Envelope Curve	Soft knee or hard knee
Preset

Use this field to choose and enter presets.

Audition

Click on this to hear the results of the command on the first three seconds of the selected audio.

See Also:

Compressor/Gate

Limiter

Expander/Gate

Interactive graph

Stereo handling

An introduction to dynamics processing


Stereo Handling

The dynamics processors offer two choices for processing of stereo signals:

Option	How it works
Maximum	The left and right channels are adjusted equally according to the maximum of the left and right channel signal levels.
Side Chain	The left channel volume alone is used to drive the effect, which is applied only to the right channel.  This can be used, for example, to automatically lower the level of background music when a voice-over kicks in.
See Also:

An introduction to dynamics processing

Compressor/Gate

Limiter

Expander/Gate

Dynamics Processor

The interactive graph

Glossary


Interactive Graph
The Interactive Graph

Three of the four dynamics processors (excluding the limiter) include a graph that lets you draw the envelope curve that defines the threshold levels and ratios.  You adjust the envelope by moving the nodes that define the curve.  Here’s how:

To do this	Do this
Move a node	Drag it to a new location with the mouse.  Dragging with the left button down will cause the node to follow the cursor precisely.  When the right button is used, a large movement by the mouse results in a small movement by the node, allowing more accurate control of the node’s location.
Zoom in and out of the top right corner of the graph	Click on the text ‘Zoom-in’ and ‘Zoom-out’
Add a node	Click a short distance away from the existing nodes
Erase a node	Press and hold the Shift key, and then click on the node

Note that you cannot delete the starting or ending envelope points.  Also, keep in mind that the graph does not reflect the effect of master gain on the output levels.

The “knee” refers to the bend in the envelope curve. A soft knee transition converts a hard corner into a smooth curve that kicks in more smoothly and gradually on signals surpassing the threshold.  Soft knee compression curves are suited for vocals, guitars and other non-percussion instruments, as well as entire mixes. Hard Knee compression curves are better suited for drums and other percussion instruments.

See Also:

An introduction to dynamics processing

Compressor/Gate

Limiter

Expander/Gate

Dynamics Processor

Stereo handling

Glossary


Glossary

Term	Meaning
Attack Time	The time it takes to respond to increases in the input signal level
Compressor	An audio effect that reduces the dynamic range of an audio signal
dB (decibel)	a unit of measurement that expresses the relative levels of two electrical voltages
Dynamic Range	The difference from the highest and lowest levels of a varying audio signal
Expander	An effect that increases the dynamic range of an audio signal, by reducing the signal level any time it drops below a specific threshold
Gain	The amount of amplification applied to an audio signal
Gate	A device that increases the dynamic range of an audio signal by cutting off a signal when its level falls below a specific threshold
Hard Knee	An input/output curve that changes slope suddenly at thresholds
Harmonic Distortion	The addition of harmonics that were not present in the original signal, due to changes in the shape of the waveform
Limiter	An effect that prevents an audio signal from exceeding a specific level
Noise Gate	See Gate
Ratio	The factor by which gain exceeding the threshold is reduced or expanded
Release Time	The time it takes to respond to decreases in the input signal level
Soft Knee	An input/output curve that changes slope gradually around thresholds
Threshold	The level at which the compressor or expander starts to operate
Transient	A momentary high peak level
Waveform	A graphical representation of an electrical signal
See Also:

An introduction to dynamics processing

Compressor/Gate

Limiter

Expander/Gate

Dynamics Processor

Stereo handling

The interactive graph