compressor gain control principles

A short compendium on digital audio compression techniques.

Basic compressor configurations

Compression vs. limiting

Technically speaking the same principles are used in audio signal limiting and compression processors but just the transfer curves and envelope follower settings are different. Ultra fast attack rates and high ratio amounts are used for limiting purposes which causes just very few peaks to pass on a certain threshold.

In digital implementations limiting processors can be more strict due to look-ahead and clever gain prediction functions which guarantees that no peak information passes the threshold. That is called brickwall limiting then.

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soft-knee compression and beyond

preview

transfer curves

Beside the envelope design for the control signal the compressors transfer curve is the most influencing part speaking in terms of the resulting sound impression. If we ignore any time dependend behaviour of the compressor for the moment then it basically works like this: Signals at a level below a certain threshold are passing through the device unaltered. Reaching the threshold level the input signal gets lowered by a certain ratio.  The result is a so called “hard-knee” transfer curve. [Read more…]