With non-square LFO waveforms, gives the effect of the sound source moving from place to place in stereo or more channel setups. Some Thomas Organ Vox amps have this as a built in effect. Compression makes soft inputs louder, and loud ones softer, giving a one-level kind of sound with lessened dymanics. This is effectively volume control with the level determined by the negation of the averaged envelope of the input level. The Electro-Harmonix Black Finger was among the first compressors in the early 1970s, along with the Maestro sustainer.
Expansion Makes loud sounds louder and soft ones softer.
Effectively volume control with the level determined by the averaged envelope of the input level. Only the peaks of the input waveforms get compressed, not the overall level of the waveform envelope. Effectively, there is no averaging of the envelope and the instantaneous waveform level is compressed. Noise gating modulates the output off when the input level is below a threshold. This gives an output which perceptibly rises in level with each new note envelope, reminiscent of a tape recording played backwards.