Digital Sound & Music: Concepts, Applications, & Science, Chapter 6, last updated 6/25/2013
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Figure 6.24 LFO controls on a synthesizer
Envelopes 6.1.8.7
Most synthesizers have at least one envelope object. An envelope is an object
that controls a synthesizer parameter over time. The most common application
of an envelope is an amplitude envelope. An amplitude envelope gets applied
to the signal amplifier for the synthesizer. Envelopes have four parameters:
attack time, decay time, sustain level, and release time. The sustain level
defines the amplitude of the sound while the note is held down on the
keyboard. If the sustain level is at the maximum value, the sound is played at
the amplitude defined by the master volume controller. Consequently, the
sustain level is typically an attenuator that reduces rather than amplifies the
level. If the other three envelope parameters are set to zero time, the sound is simply played at
the amplitude defined by the sustain level relative to the master volume level.
The attack and decay values control how the sound begins. If the attack is set to a positive
value, the sound fades in to the level defined by the master volume level over the period of time
indicated in the attack. When the attack fade-in time completes, the amplitude moves to the
sustain level. The decay value defines how quickly that move happens. If the decay is set to the
lowest level, the sound jumps instantly to the sustain level once the attack completes. If the
decay time has a positive value, the sound slowly fades down to the sustain level over the period
of time defined by the decay after the attack completes.
The release time defines the amount of time it takes for the sound level to drop to silence
after the note is released. You might also call this a fade-out time. Figure 6.23 is a graph showing
these parameters relative to amplitude and time. Figure 6.24 shows the amplitude envelope
controls on a synthesizer. In this case, the envelope is bypassed because the sustain is set to the
highest level and everything else is at the lowest value.
Figure 6.25 Graph of ADSR envelope
Max Demo:
ADSR
Envelopes
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