Envelopes (ADSR)
A waveform describes the oscillator's shape. An envelope describes how a parameter changes over time after a key is pressed and released. Use it to decide whether a sound starts sharply, settles quickly, holds, or leaves a tail.
The Four Stages
ADSR stands for Attack, Decay, Sustain, and Release. Together they describe the sound from key press to key release.
Attack
How quickly the sound reaches full volume after you press the key. Short attack gives drums and plucks a clear start; long attack makes pads and strings fade in. If a part feels late, check its attack before moving the MIDI notes.
Decay
How quickly the sound drops from its peak to the sustain level. Short decay = percussive, sounds die quickly. Long decay = more gradual, natural fade after the initial hit.
Sustain
The volume level held while the key is pressed (after attack and decay). This is the only stage that's a level, not a time. Full sustain = organ-like (sound stays at full volume). Zero sustain = pluck-like (sound dies away even while holding the key).
Release
How quickly the sound fades after you let go of the key. Short release = sound stops immediately (staccato). Long release = sound lingers and trails off (reverb-like tail).
ADSR Examples
Different combinations create completely different instruments:
Piano
Immediate attack with a natural decay that sustains while held.
Pad / Strings
Fades in gently, holds at a consistent level, trails off smoothly.
Pluck / Stab
Instant hit that dies away quickly regardless of whether you hold the key.
Organ
Full volume while held, silent the instant you release. On/off like a switch.
Envelopes Beyond Volume
ADSR does not only control volume. In many synths, an envelope can modulate a parameter such as filter cutoff, pitch, or wavetable position. Filter cutoff is a particularly useful example because the envelope can change the harmonic content at the start of each note.
Filter Envelope
Controls how the filter opens and closes over time. A fast attack and medium decay on a low-pass filter creates the classic "wah" at the start of each note - bright attack that mellows quickly.
Pitch Envelope
Controls pitch over time. A very short pitch sweep at the start of a note creates a "zap" or "laser" effect. Subtle pitch envelopes add a natural feel to synth sounds.
Production Tip
If a synth sound feels lifeless, try adjusting the attack and release first. Even tiny changes - adding 20ms of attack to soften the start, or extending the release slightly so notes overlap - can make a mechanical sound feel organic. The ADSR is often more important than which waveform you choose.
Try it
Keep the harmony the same and change only the envelope shape.
Same harmony - envelope shape changes the character entirely.
Key takeaway
ADSR envelopes shape how a parameter changes over a note's lifetime. Attack and release control the edges, decay and sustain control the middle. They turn static tones into expressive, dynamic sounds.
Next: adding cyclical movement and animation to sounds - LFOs.
Hear envelope shapes in action
Starts generates notes with different velocities and lengths, showing how envelopes shape each one.