Effects documentation

Compressor

An insert compressor based upon a minimal electronic circuit.

Description

The compressor is designed to loosely model a circuit I designed myself. It is like a pedal or what you might find in a channel-strip.

It isn't designed to function as a limiter and it doesn't have instant response, look-ahead, low distortion or any of that stuff. That is exactly what makes it useful.

Screenshot

Compressor screenshot

Parameters

Attack
Time for level to decrease to threshold.
Release
Time for level to increase back toward unity.
Threshold
This parameter is actually inverted compression depth.
The "threshold" parameter corresponds to the gain reduction given zero attack and a 0 dB input. For each halving of input amplitude (-6.02 dB) the compression depth is likewise halved.
Mix
Mixture between uncompressed and compressed signals.
Gain
Make-up gain applied after compression to bring the signal back up to the desired level.
Mode
Mode A provides direct feedback which leads to non-linear behavior; this mode matches the analog circuit and is useful for its higher distortion and non-linear timing behavior.
Mode B scales feedback by the compression envelope which squares and linearizes the response such that the envelope timings are accurate. This mode provides a significant reduction in distortion and a more typical general purpose compression effect.
Side-chain
Enables side-chain (channels 3,4) input. With this switch off the side-chain is fed back from the output.
Stereo-link
With this switch enabled the max gain reduction level from left and right channels is applied to both.

UI

The peak and gain reduction meters are both peak (discrete) meters with an AR envelope: 1 ms attack, 250 ms release per 40 dB. These are not high accuracy meters but serve to aid the adjustment of local (inside the effect) dynamics parameters.

These meters include a peak text display which shows the peak level of the meter over the past 200 ms window.

The meters can be clicked to adjust the displayed range. The current version does not store this setting and it will reset to default when opening the GUI.

Comments

Although this compressor does not include a built in "look ahead" feature, it does include a side-chain input switch.

By applying a delay to the main input signal the performance of the compressor can be improved significantly. This is generally counter-productive where high distortion is a desired trait. When used for general purpose compression an external delay can be used to reduce distortion beyond the limit of the compressor on its own.

The side chain input can also be filtered in various ways to target the action of the compressor. A high-pass filter is often applied here to allow bass frequencies to pass without affecting the dynamics of other elements.