Soft-knee dynamic range compressor intended to emulate a typical stompbox effect for guitar. The feedback topology lends itself well to the “squish” typical from the guitar compressor.
By it’s nature it has a soft knee characteristic for low ratio settings. The “ratio” setting is more of a knee radius setting since a feedback compressor approaches a high compression ratio as input signal level increases.
Revision 2 added some extra modes:
1) Choose between log-linear or the other continuously increasing ratio transfer function.
2) Choose hard or soft knee (soft knee was added to address higher threshold settings)
3) Parallel compression (schematic not updated). The 6th analog input serves as a wet/dry mix so transients can be better preserved while gaining advantage of sustain added from the compressed path.