The Norrland E=mcompressor is based on an original design by M. Blencowe around the LM13700 Operational Transconductance Amplifier (OTA). Most off-the-shelf compressors that are OTA based are noisy. This is due to the nature of the IC. In this design, the OTA is placed in the feedback loop of the TL072 opamp. This reverses the gain of the OTA as opposed to the gain you dial in. When the circuit is running at full gain, the amount of feedback from the OTA is restricted, reducing the overall noise. The side chain of this circuit is feedforward instead of the more common feedback approach. This enables the possibility to control the attack time, which is usually locked to a very fast attack. The attack knob on many compressors is a misnamed release knob. In order to ensure that your signal does not go dull on high compression settings, a treble boost is also on board.
Level: compressing a signal turns down its volume. The level knob controls the make-up gain to bring the volume level back to normal.
Ratio: during compression this decides how much the gain is reduced. At the highest setting it maintains your signal at a constant level independent of the input level which is perfect for maximum sustain.
Threshold: the higher this is set the louder the input signal has to be before it is compressed.
Attack: the time it takes before the compression begins.
Release: the duration of the compression.