Sound envelope

See also: Envelope

The sound envelope is one of the properties of a its instrumental returning more precisely to the evolution of sound Amplitude (its volume) during time.

It can be represented by a bell-shaped curve which presents three parts:

the attacks is the ascending segment of the curve;
the maintenance is the upper part of the bell;
the falls is the downward segment.

This type of curve is called curved Enveloppe because it wraps the signal. The rising part constitutes the attack and can be very different according to the type of instrument (with wind, with cord, percussion…). The second part called “ sustain ” in English, is the body of the note, and often constitutes the longest part of the note except for the notes of the percussion instruments. The third part is also of duration and very variable form according to the type of instrument.

The instruments make it possible the Musicien S to influence these three parts. Thus, the way of striking the keys of a Piano will change the attack of the note whereas the pedals modify the final part (the fall). Each of the three parts can have a very different spectrum what still contributes to increase the diversity of the sounds. The Harmonique S do not evolve/move indeed together. Low the Fréquence S in general tends to last longer than high with the result that the color of the sound perceived at the beginning of the note is not the same one as at the end.

Wrap ADSR

Envelope ADSR ( has ttack D ecay S ustain R elease) is a modeling by four parameters of the sound envelope of a sound generated by a Synthétiseur. That makes it possible to describe how the instrument must make evolve/move the amplitude (volume) sound created, according to time.

The four parameters are:

has ttack: the attacks described the time necessary with the sound to reach its maximum amplitude, after having pressed on a key of the synthetizer.
D ecay: the decline indicates time beyond the peak, to reach the moment when the sound enters in phase of maintenance,
S ustain: the maintenance describes the preserved noise level as long as the key is maintained inserted. If the Claviériste slackening the key too early, the sound enters directly in relaxation .
R elease: as of the relaxation of the key, this parameter indicates the speed with which the sound decreases to die out completely.

There exist synthetizers which have additional parameters for a more precise description of the envelope.

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