Sound decay is the rate at which a sound fades to silence. It is a fundamental element in describing the lifespan or envelope of a sound, representing the final stage after the initial attack and potential sustain.
Every sound, from a single note played on an instrument to ambient noise, has a characteristic evolution over time. This evolution is often described using a model consisting of three primary phases: attack, sustain, and decay.
The Phases of Sound: Attack, Sustain, and Decay
Understanding sound decay is clearer when viewed in the context of the complete sound envelope:
- Attack: This is the initial phase when a sound begins. According to the reference, attack transients consist of changes occurring before the sound reaches its steady-state intensity. It's how quickly the sound reaches its peak loudness. Think of the sharp impact of a drumstick or the initial pluck of a guitar string.
- Sustain: Following the attack, if the sound maintains a relatively constant loudness, it is in the sustain phase. The reference describes sustain as the steady state of a sound at its maximum intensity. This phase is prominent in sounds that are held, like a sustained note on a violin or a blowing wind.
- Decay: As defined in the reference, decay is the rate at which it fades to silence. This is the phase where the sound's intensity decreases until it is no longer audible. The rate of decay can vary greatly depending on the sound source and the environment. A piano note decays relatively quickly, while a church bell might ring and decay slowly over a minute.
The Importance of Decay Rate
The specific rate of decay significantly impacts the perceived character of a sound.
- Fast Decay: Sounds with fast decay are often perceived as percussive or abrupt. Examples include plucks, hits, and short, sharp notes.
- Slow Decay: Sounds with slow decay are often perceived as smooth, sustained, or resonant. Examples include bowed strings, sustained wind instruments, or sounds in highly reverberant spaces.
In music and audio production, controlling or shaping the decay phase is crucial for defining the rhythm, feel, and texture of a piece. Techniques like using volume envelopes, compression, or reverb directly influence how quickly or slowly sounds fade away.
| Phase | Description (Based on Reference) | Characteristic Action |
|---|---|---|
| Attack | Changes before reaching steady-state intensity | Sound begins and rises |
| Sustain | Steady state at maximum intensity | Sound holds intensity |
| Decay | The rate at which it fades to silence | Sound decreases intensity |
The decay phase is essentially the tail end of the sound, governing its final moments before silence.
