The ramblings of an IT Professional, Long Distance Runner, Creative, and Maker of Stuff.
Modular Synthesizer Project
Part 3 - Envelope Generator
26th October 2020
 2 min read

Finally stuff gets a bit more interesting - envelope generators. These are the core building block for wave shaping. Typically they are used to control VCA's (Voltage Controlled Amplifiers) or VCF's (Voltage Controlled Filters) so that the sound changes over time from the initial trigger.

The most common application is to create different phases of a sound over time:

  • Attack - The rate at which the envelope goes from closed to open
  • Decay - The rate at which the envelope starts to drop from open to the release level
  • Release - The level at which the envelop stays after the decay
  • Sustain - The rate at which the envelop drops to closed from the decay level

ADSR Envelope
ADSR Envelope

An ADSR is the most common type of envelope, but I wanted to keep things simple initially, so I opted for an AR envelope - Attack + Release. Hence control over the rate of attack and rate of release.

I'd use the AR envelope with the VCF and VCA (that I'll cover in a future write-up) and would trigger these on the note-on/off gate. Hence the envelope would kick into action based on when a key (or note-on event) was handled.

Yet again I'd turn to LookMumNoComputer for a bit of inspiration. A nice and simple TL072 op-amp based circuit which acts as a comparator between input and outputs, with a capacitor and couple of potentiometers to control the charge/discharge rates.

This module nicely fitted within a 4HP panel, so a bit more slimline. Beer based fascia from Beavertown Neck Oil.

Front Panel
Front Panel

The controls are pretty simple:

  • Gate In jack - Gate input signal (eg from sequencer or MIDI2CV), when the gate goes high (on) the attack phase is initiated and held open until the gate goes low (off), at which point the release phase is initiated.
  • Envelope Out jack - The CV (0-10v) that rises and falls (rate) based on the attack and release settings.
  • Attack pot - The speed / rate at which the envelope rises to open (10v). Slow attack = strings, fast attack = bass
  • Release pot - Same concept as attack, but the speed / rate that the envelope falls to closed (0v) after the gate is closed.

More blog posts in this series: