Some basics if anyone wants to know.
A compressor is a processor not an effect. It is a dynamic processor used to control the level of signal. Here are the basic controls and uses.
Threshold (sometimes input):
This determines the trigger level of the compressor. If set to -10dB, any signal going over -10dB will activate the compression circuit.
Ratio:
This determines the amount of compression. If set at 2:1, any signal crossing the threshold will be reduced by 1/2. This would be very little compression. 4:1 to 8:1 is a typical compression setting for bass. If set to 10:1 or higher you are basically limiting. At that point no signal will go past the level set by the threshold. (sort of... see attack)
Attack:
This determines how quickly the compression circuit is activated. If set to 30ms (milliseconds), the compressor will allow signal to cross the threshold point for 30ms before activating. If set to 0ms, as soon as signal crosses the threshold it gets squashed. A fast attack will catch that transient peak and protect your equipment if needed. A slower attack will let that initial pop go through and produce a more percussive sound.
Release:
Like attack, this determines how long after the signal goes below the threshold the compression stays activated. If set wrong with the attack you can get pumping or breathing. Here is something explaining that I found online.
When a compressor is making large changes to the input signal (10 to 12 dB or more), the noise floor will also rise and fall with the signal level. When this noise signal rises and falls drastically between signals, such as a heavily compressed, noisy drum track, you might hear the noise level breathing between drum hits. One solution to this breathing problem is to turn up the release time. This way, the noise floor won't have time to rise between drum hits.
However, if the Release time is too long, lower level signals after the peak will be lost as the compressor slowly stops reducing gain. This is called pumping as the lower level signals (noise included) slowly fade back up to their normal signal level. The secret to avoiding these problems is to achieve a balanced release time on the input signal.
Output:
A compressor reduces the level of signal. The output is used to compensate for that loss of level.
Some units don't have all these controls. Some have more. Often the attack and release are not available. In these units the attack and release are pre set to a moderate setting.
(Message edited by matthew90046 on August 03, 2005)
