"The SW912 Envelope Follower produces two functions, which can be used separately or in conjunction. The follower circuit signal input presents a control voltage output (DC) proportional to the average amplitude of the AC input signal. The second function, a Schmitt trigger, generates a V-trigger above a threshold voltage (comparator), when a slowly varying or DC voltage is introduced at the control input jack. The normalling of the control output of the follower circuit to the control input of the Schmitt trigger circuit allows both control voltage and trigger to be generated from a single variable source.
MUSICAL APPLICATION
THe SW912 Envelope Follower is an extremely useful module for interfacing external sources with the many functions of the synthesizer, which require both control voltages and triggers to function. Filter or amplitude variations can be achieved by routing the audio signal to both the processing modules and the Envelope Follower. The control voltage of the follower circuit can raise or lower the cutoff frequency of a voltage controlled filter. At the same time, the Envelope Generator can be triggered by the V-trigger output of the follower, causing a VCA to gate the original signal above a certain amplitude. This latter operation can be very useful as a noise gate, closing down an audio signal when the level drops below a nominal setting. One further use involves generating random triggers from the Envelope Follower by utilizing white noise or pink noise as a signal input and carefully setting the threshold level to achieve a speed of trigger selection."
