AMSTRAD CPC464 User Manual page 143

Up to five <envelope sections may be supplied, and each may take one of the forms : step count,step
sizep,qpause time>
or: =&one periodp,(pause time>
The first form specifies an incremental change relative to the current tone period setting. The second
form specifies an absolute setting for the tone period. Where : step count, gives the number of steps
in the section - an (integer expression in the range 0..239.
step size, gives the amount by which to vary the tone period at each step in the envelope - an
<integer expression yielding a value in the range -128.. + 127.
<pause time> gives the time to wait between steps - an <integer expression, specify-ing the time in
0.01 second units. The expression must yield a value in the range 0..255 (where 0 is treated as 256).
tone period, gives the new setting for the period - an (integer expression yielding a value in the range
0..4095.
The SOUND command sets the initial tone period, and may specify one of the fifteen tone envelopes.
If no envelope, or an envelope which has not been set up is specified, then the tone remains constant
throughout the sound.
A tone envelope has no effect on the duration of the sound. If there are steps remaining in the tone
envelope when the sound finishes, they are simply abandoned.
A repeating tone envelope will be restarted each time it finishes until the sound terminates.
The expressions in the tone envelope are evaluated when the command is executed and the results
stored away for future use. Using the tone envelope does not cause the command to be re-executed.
Each time a given tone envelope is set, its previous value is lost. Changing an enve-lope while a
sound using it is active or pending will produce indeterminate (but possibly interesting) effects.
Specifying an envelope with no sections cancels any previous setting. Any further use of the envelope
will be ignored and the default used instead.
Associated keywords: E N V , S O U N D
ENV
E N V < e n v e l o p e n u m b e r > [ , < e n v e l o p e s e c t i o n s > ]
1 0 E N V 1 , 1 0 0 , 2 , 2 0
2 0 S O U N D 1 , 1 0 0 , 1 0 0 0 , 4 , 1
COMMAND: While a sound is being generated, it is possible to vary its volume using this command.
A volume envelope consists of:
step count, step size), <pause time,
and defines how the volume is to be varied, by specifying a number of steps in the range 0..127, the
size of the step in the range -128....+127, and the pause time in 0.01 second intervals in the range
1....256.