dbx Compression 101 Manuel - Page 4

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Compression 101

Terms

Compressors are often difficult to grasp for beginning musicians and engineers. Where an

effect like pitch shifting or delay is easy to hear, compression often performs subtle changes

on a signal and can be more difficult to learn.This introduction is intended as an expanded

glossary, which shows what the controls on the compressor's front panel are doing to the

input signal.

Threshold

The THRESHOLD knob sets the level where compression will begin. As long as the input

signal level is below the Threshold level, the compressor will do nothing to the signal. Once

the input signal crosses the Threshold, the compressor will begin compressing at a ratio set

by the ratio control.

Ratio

The RATIO knob controls the amount of compression, which will happen once the input

signal crosses the Threshold level, described above. Ratio controls how much the input

signal will be reduced as a ratio of the input signal level. For example, if the compression

ratio is set for 6:1, the input signal will have to cross the threshold by 6 dB for the output

level to increase by 1 dB. the maximum setting is typically labeled: 1 (infinity to 1),a nd is

also called Limiting.This means that the output signal won't increase at all, no matter how

far above the threshold the input signal goes.

Attack

The ATTACK knob controls the amount of time before compression starts after the

threshold is exceeded by the input signal.The range of this control can go anywhere from

very slow (about 1dB/Sec) to very fast (about 400dB/Sec). Long attacks are useful for

percussive sounds, where shorter attacks are good for melodic parts like vocals and strings.

The Attack control is also useful for keeping the transients on percussive drum or bass

sounds. Experiment with different short attack times on snare drums to get more or less of

the "stick" attach.

Release

The RELEASE knob controls the amount of time the compressor takes to stop compressing

after the signal crosses below the threshold. the range of this control can be from approxi-

mately 4000dB/Sec to 10dB/Sec. Short release times are good for percussive, punchy

sounds, where longer release times can make compression less obvious on vocals.Adjusting

the release time may be necessary when using extreme compression and "pumping" or

"breathing" is audible, or if lower level signals after peaks are getting lost. See also the

section on pumping and breathing explained below.

Output

The OUTPUT knob controls the level of the compressor's output. The Output control is

useful for making up gain, which was reduced by the compression circuit, or matching the

input level of a mixer or recorder. If the Gain Reduction meter shows that the input signal

is being attenuated by -6dB, then the Output control generally should be set around +6dB.

This control is disabled if the [BYPASS] button is pressed.

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Compression 101 - November 1998