Analogue versus Digital. Some things are just better. And with the ADSR we decided to go analogue. When you need a nice clean signal, free from digital artefacts, there’s nothing like the charging up of analogue components.
The ADSRs primary role in the modular synthesiser is to take a Gate input and generate dynamic control voltages which change over time. The Gate is usually provided by a sequencer or keyboard, when a key is pressed the gate goes high, which the key is released the gate goes low. The code within the module translates this gate signal to the various stages of the control envelope: Attack, Decay, Sustain and Release. This control voltage out can then be patched into a VCA to control volume, VCF to control frequency cutoff or VCO to control other modulation parameters such as FM or PWM.