The <envelope number is an <integer expression, yielding a value in the range 1..15 specifying the
volume envelope toset.
Up to five (envelope sections, may be given. Each may take one of the forms:
step count,step size,,cpause time, *
or: =chardware envelopeb,<envelope period,
The first form specifies an envelope section under software control, where parameters are :
step count gives the number of steps in the section - an integer expression in the range 0..127.
step size> gives the amount by which to vary the amplitude at each step in the envelope - an integer
expression) in the range -128....+127.
or : if the step count is zero, then the value to set the amplitude to - that is an absolute setting.
<pause time) gives the time to wait between steps - an &teger expression specifying the time in
l/lOOth’s of a second. The expression must yield a value in the range 0....255 (where 0 is treated as
256).
The second form specifies an envelope section to be executed directly by the sound hardware, where :
<hardware envelope, is the value to be set into the envelope shape register (register 15, octal).
<envelope period, is the value to be set into the envelope period registers (registers 13 & 14, octal).
Hardware envelope settings do not have an associated pause time, so the next section of the envelope
is immediately executed. It is advisable therefore that the next step should have a pause of a
suitable length. If there is no next step, then a pause of 2 seconds is taken.
The
SOUND
command sets the initial volume, and may specify one of the fifteen volume envelopes.
If no envelope, or an envelope which has not been set up, is specified, then the volume remains
constant throughout the sound.
Setting a step size, of zero with a non-zero step count causes the current volume setting to be
maintained.
The expressions in the amplitude envelope are evaluated when the command is executed and the
results stored away for future use. Using the amplitude envelope does not cause the command to be
re-executed.
Each time a given amplitude envelope is set, its previous value is lost. Changing an envelope 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:
ENT, SOUND
Summary of Contents for CPC464
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Page 102: ...PRINT 10 AND 12 Results in 8 PRINT 10 AND 1000 Results in 8 again ...
Page 118: ...TO DO DRAW THIS PAGE ...
Page 219: ...actual value may be made to vary during the execution of a program ...
Page 240: ...Text and WINDOW planner Mode 2 80 Columns ...
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