Compresor parameters: Compression curve
From Audacity Development Manual
This page goes in more detail about the "Compression curve" parameters of the Compressor.
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Parameter list
The table below lists the compressor parameters, and illustrates its effect with a test tone as input. All time smoothing parameters are set to zero.
For less confusing illustrations, the maximum ratio was increased to 10000. In practice, the actual maximum (100) should be more than enough. For higher ratios, consider using the limiter instead.
Compression curve settings Setting/Description Editor Waveform (dB) Waveform (linear, zoomed) Spectrum Comments Input N/A 
A 440Hz sine wave with triangular envelope, ramping up from -60 dB to 0 dB and back. Threshold 
Equivalent to hard clipping. Strong harmonic distortion. Make-up gain 
No image No image Amplifies the signal after compression, here by 5 dB. Knee width 
Introduces instantaneous smoothing, gradually applying compression even under the threshold. Not as effective as time smoothing, but without its side effects on audio preceeding and following the compression moments. Here somewhat reduces the higher distortion harmonics. Ratio 
Another means of instantaneous smoothing. Compression isn't applied below the threshold, but there can't be a clear ceiling anymore.
