How much will the signal be compressed once it has passed this threshold level ? This is controlled by the ratio . The higher the ratio , the greater the compression . The easiest way to show you how the ratio works is to show you some numbers :
• 1:1 - there is no compression .
• 2:1 - for every 2 dB of sound above the threshold , you get 1 dB of output above the threshold . Therefore , if the signal exceeds the threshold by 10 dB , the compressor reduces this signal so that it is now 5 dB above the threshold .
• 8:1 - for every 8 dB of sound above the threshold you would get 1 dB of output above the threshold . Therefore , if the signal exceeds the threshold by 16 dB , the compressor reduces it so that only 2 dB is exceeded .
Attack It is the time it takes for the compressor to act on the input , once the sound level has exceeded the threshold level . It is usually measured in milliseconds ( ms ).
Release This is the time it takes for the compressor to let the signal return to normal once the threshold level has dropped . Again , it is usually measured in more .
Output Gain ( Make-up Gain ) If the audio signal has been compressed , the overall signal level will be reduced . Increasing the output gain raises the level output from the compressor , so that the volume can more easily adjust to the levels of the rest of the tracks in the mix .
A widely used technique to control the mixture is known as “ Level Matching ”. And this is executed by applying the “ Make-Up gain ”
Knee Soft Knee compression is lighter on the sound as it passes through the audio compressor . Hard compression is a more immediate and obvious effect .
Lookahead Faced with having to compromise between slow and fast attack rates ( the former produces smoothsounding gain changes , while the latter is capable of picking up transients ), is where the lookahead comes into play .
It overcomes this problem by splitting the input signal into two paths , i . e . delaying one . The real-time audio is analyzed by the compressor before the information obtained from its evaluation is applied to the delayed signal . That delayed signal is what is sent to the compressor for compression .
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