Envelope
Definition
The shape of a sound's amplitude over time, typically described in four stages: Attack, Decay, Sustain, and Release (ADSR). The envelope determines how a sound begins, develops, and ends, and is a foundational concept in both synthesis and dynamics processing.
In Simple Terms
The shape of how a sound starts, sustains, and fades away. A piano has a sharp start and a long fade. A pad synth has a slow rise and an even slower fade. Understanding envelopes helps you shape how every sound feels.
In Practice
A piano note has a fast attack (the hammer hits the string immediately), a short decay (the initial brightness fades), a sustain (the note rings at a stable level while the key is held), and a natural release (the string dampens when the key is released).
Sources & Verification
- Smith, J. O. — Spectral Audio Signal ProcessingStanford CCRMA, 2011
- Pohlmann, K. C. — Principles of Digital Audio (6th ed.)McGraw-Hill, 2011
Last verified: 2026-05-05