TLDR:

"Envelopes modulatate a destination over time - the most common stages of this shape are attack, decay, sustain, and release."

What Is an Envelope?

An envelope is a control voltage that changes over time, usually in response to a gate or trigger. It defines how something behaves dynamically - like how a note fades in, sustains, and fades out. Envelopes are essential for giving your synth patches movement and life.

They’re most commonly used to control amplitude (via a VCA) or filter cutoff, but you can patch them anywhere you want gradual or shaped change. They are GENERALLY positive voltage that returns to zero, that comes from a trigger source.

ADSR - The Classic Envelope

• Attack: How long it takes to reach full level after a note is triggered.
• Decay: How long it takes to drop to the sustain level after the attack phase.
• Sustain: The level held while a key or gate is held down. It’s not time-based - it’s a level.
• Release: How long it takes to fade out after the gate is released.

Other Envelope Types

• AR (Attack/Release): Simple two-stage envelope - great for percussive or snappy modulation.
• AD (Attack/Decay): Common in trigger-only envelopes (think drum synths or snappy mod).
• Looping Envelopes: Acts like an LFO, but shaped like an envelope - great for organic repeating modulations.
• Function Generators: More complex or flexible envelopes that can behave like envelopes, LFOs, slew limiters, and more.

Where to Use Envelopes

• Amplitude: Classic use - shape how loud the sound gets over time (via a VCA).
• Filter Cutoff: Create dynamic filter sweeps or plucks.
• Pitch: For quick zaps or pitch drops (think kick drums).
• Modulation Depth: Use an envelope to control how much an LFO is affecting something.

Envelopes are your sculpting tools. They can be subtle or dramatic, slow or snappy - and once you start chaining and modulating them, things get deep fast. Think of them as the emotion behind the motion.

Great Video