Commodore 128 Programmer's Reference Manual page 619

C128 HARDWARE SPECIFICATIONS 609
ATTACK:
DECAY:
SUSTAIN:
RELEASE:
10
8
10
9
($A)
($A)
500 ms
300 ms
750 ms
Note that the tone can be held at the intermediate SUSTAIN level for as long as
desired. The tone will not begin to die away until GATE is cleared. With minor
alterations, this basic envelope can be used for brass and woodwinds as well as strings.
An entirely different form of envelope is produced by percussion instruments such
as drums, cymbals and gongs, as well as certain keyboards such as pianos and
harpsichords. The percussion envelope is characterized by a nearly instantaneous attack,
immediately followed by a decay to zero volume. Percussion instruments cannot be
sustained at a constant amplitude. For example, the instant a drum is struck, the sound
reaches full volume and decays rapidly regardless of how it was struck. A typical
cymbal envelope is shown below:
ATTACK: 0 2 ms
DECAY: 9 750 ms
SUSTAIN: 0
RELEASE: 9 750 ms
Note that the tone immediately begins to decay to zero amplitude after the peak is
reached, regardless of when GATE is cleared. The amplitude envelope of pianos and
harpsichords is somewhat more complicated, but can be generated quite easily with the
ADSR. These instruments reach full volume when a key is first struck. The amplitude
immediately begins to die away slowly as long as the key remains depressed. If the key
is released before the sound has fully died away, the amplitude will immediately drop to
zero. This envelope is shown below:
j ATTACK:
DECAY:
SUSTAIN:
"j RELEASE:
1
0
9
0
0
2 ms
750 ms
6 ms
Note that the tone decays slowly until GATE is cleared, at which point the
amplitude drops rapidly to zero.
The most simple envelope is that of the organ, When a key is pressed, the tone
immediately reaches full volume and remains there. When the key is released, the tone
drops immediately to zero volume. This envelope is shown below: