Acoustic Envelope

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This is another important cue in addition to spectrum that allows us to discriminate one sound from another.

 

From the moment a sound begins until it ceases there is usually a characteristic variation in the sounds overall intensity or amplitude.

 

In its most simplified form three parts of this acoustic envelope can be distinguished:

 

The initial attack portion or transient is very important in providing cues as to the nature of the sound being started.

The transient is followed by a period of more or less stable internal dynamics often described as a sustain.

The sound finishes with some kind of decay to silence.

    Sound Examples:  

clarinet

attack only

sustain only

decay only

 

An envelope more commonly used in electronic music instruments is the ADSR which provides for an attack, a decay to some sustain level and a release to silence:

 

Amplitude fluctuations and the speed at which these fluctuations occur in each of these parts of the envelope account for a great variety in the perception of a timbre