The Pittsburgh Modular ADSR is a four stage envelope generator with independently adjustable Attack, Decay, Sustain, and Release stages. This module does one thing amazingly well. The ADSR smooths the shape of the incoming gates and triggers to produce a more expressive instrument. The ADSR output can be used to control the amplitude of an oscillator, the cutoff frequency of a filter or any other function on a module that accepts control voltages.
The functionality of the ADSR is simple. The incoming gate or trigger signal passes through each of the four stages to output an envelope. When the ADSR module receives a gate or trigger signal, the attack determines the amount of time needed for the envelope generator to reach the peak output voltage and move on to the decay stage. Decay sets the amount of time needed to transition to the level set by the sustain knob. The sustain level is maintained as long as the incoming gate remains on or high. Once the incoming gate goes low or off, the release stage takes over. The release knob sets the time needed to close the envelope and return the ADSR output to 0 volts.