Reduces the dynamic range of the input audio signal by "compressing" all amplitudes which exceed a specified threshold. The compression factor is adjustable (unlike the "limiter", which is, in essence, a compressor with infinite compression ratio). A delay buffer is incorporated to give the compressor a "look-ahead" capability, improving its effectiveness in some situations. The behaviour of the compressor can be adjusted via its Parameter Window as summarised in the following table. Parameter Purpose "Threshold" slider Sets the compressor threshold. The purpose of the compressor is to modify the amplitude of all signals which exceed this threshold. "Ratio" slider Sets the compression ratio. If the signal amplitude exceeds the compressor threshold, it will be reduced by this factor (in the dB scale). "Averaging" slider Sets the averaging time for the mean-square level measurement. "Attack" slider Sets the Attack Time for the compressor's gain smoother. "Release" slider Sets the Release Time for the compressor's gain smoother. "Delay" slider Sets the delay length for the "look-ahead" buffer. "Output Gain" slider Adjusts the amplitude of the output signal, after the compression has been applied.
The look-ahead compressor is implemented by measuring the mean-square level of the audio signal and applying an automatic gain control to a delayed version of the raw signal, where the gain is based on the relative values of the mean-square measurement and the specified threshold and compression ratio. See [Zo] chapter 7 for a detailed explanation.
