AMSTRAD cpc 6128 User Instruction page 416

The final part that can be added onto a SOU N D command is a seventh value that
indicates the level of noise which should be included in the sound. One point that
should be borne in mind when including noise in a sound, is the fact that there is only
one noise channel, so each subsequent noise period value overrides any previous one.
The noise can be added to a tone to give it a different sound, or can be used quite
separately, by setting the tone period (second part) of the SOU N D command to "', so
that only noise is present. This is of use in making percussive type sounds. Try this
ENT -3,2,1,1,2,-1,1
ENV 9,15,1,1,15,-1,1
FOR a=1 TO 10: SOUND 1,4000,0,0,9,3,15: NEXT
This could form the basis of a train noise. You will notice that this combines both
types of envelopes and noise.
The duration and volume parts of the SOU N D command are both set to 0 as they are
determined by the volume envelope.
Now that we can hopefully use the SOU N D, E N V and ENT commands to their full, we
can look at various other associated commands and functions.
In describing the channel number of the SOU N D command, you will remember that
by adding 64 to it, the sound was marked as 'held' so that it would remain in the
queue, without playing until released. The way in which a sound can be released is by
use of the RE LEA S E command. The word RE LEA S E is followed by a bit significant
number, where each bit is used to indicate one of the three possible channels to be
released. Once again, it is not important to fully understand this, as long as you
realise that:
4 means channel C
2 means channel B
1 means channel A
.... and a combination of channels is released by adding up the values for each of the
channels. So, to release held sounds on all three channels tlie following would be
used:
RELEASE 7
.... where 7
=
1
+
2
+
4. If no channels are held, then the RE LEA SF command is
ignored. Try the following:
SOUND 1+64,90
SOUND 2+64,140
SOUND 4+64,215
RELEASE 3: FOR t=1 TO 1000: NEXT: RELEASE 4
At your leisure.... Chapter 9 Page 43