Envelopes: Shaping Sound Over Time
Every sound has a shape in time. A piano key struck hard: the volume leaps up instantly, then starts fading immediately. A bowed cello: the volume rises slowly, holds steady, then dies away when the bow lifts.
The oscillator and waveform decide what the sound is. The envelope decides how it behaves over time.
The AR envelope
Envelopes can have many stages - some synths use four (ADSR), some use six or more. This machine uses the simplest useful model: AR, just two stages:
- A - Attack. How long the sound takes to rise from silence to full volume. A snare drum: nearly zero. A swelling string pad: several seconds.
- R - Release. How long the sound takes to fade back to silence. A plucked guitar: short. A reverberant bell: long.
Here is the shape. Follow it left to right:
That's it. Sound rises, sound falls. The attack and release times together determine whether the sound feels like a sharp hit or a slow swell.
Same waveform, different character
The difference between a "pluck" and a "pad" is almost entirely the envelope, not the oscillator. Same waveform, same frequency. The envelope alone transforms the character.
Fast attack, short release. Sharp and percussive.
Slow attack, slow release. Gentle and ambient.
Instant attack, fast release. A sharp hit that vanishes.
Try it: hear the envelope
Press Play to start the oscillator. The envelope fires automatically - attack rises to full volume, then release fades to silence.
The LFO button loops the envelope over and over, turning it into a repeating pattern - the sound repeatedly rises and fades.
Instrument presets
Different instruments have characteristic envelope shapes. The presets map directly to these:
| Instrument | Attack | Release | Character |
|---|---|---|---|
| Piano | Fast | Medium | Quick start, fading resonance |
| Organ | Instant | Instant | On/off like a switch |
| Pad | Slow | Long | Gradual swell and fade |
| Pluck | Instant | Short | Sharp percussive blip |
Try the presets. Pluck fires a sharp, percussive blip. Pad makes the same oscillator swell up and fade away gently. Identical waveform, completely different character. The envelope is doing all the work.
The click test
Listen carefully to the attack stage. Very short attack (under 5 ms) produces a click at the start - the speaker cone being shoved into motion abruptly. Longer attack (50-200 ms) gives a smooth fade-in.
The attack time alone determines whether a sound feels percussive or gentle.
- Attack = time (ms). How fast the sound appears.
- Release = time (ms). How fast the sound disappears after you let go.
Beyond volume: filter envelopes
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