Commodore VIC-20 - Page 112

from 1 to 15. We suggest you always use 15, unless you're playing
with
the amplitude as part ol a sound effect.
Each speaker has a range of 128 separate settings. To "play" a
particular note you must POKE one of the speaker settings, which
happen to be numbered from 128 to 255. If you POKE a number
lower than 128 or higher than 255 you will get no sound (which
suggests one way to interrupt a speaker while it's "on").
Here's an example of how to play a note on the VIC:
20 POKE 36878,15 SETS VOLUME AT MAXIMUM
30 POKE 36875,200 TURNS ON SPEAKER NUMBER 2
40 FOR X=1TO1000: THIS IS A1000COUNTTIME DELAY
NEXT
50 POKE 36878,0 THIS TURNS THE SPEAKER OFF
AFTER COUNTING TO 1000
RUN
The VIC uses the television speaker as its "voice," so the volume
can also be adjusted by turning the television speaker (or other
external amplifier).
ABBREVIATING THE SOUND COMMANDS
You can abbreviate the lengthy POKE commands described above
by converting these to programming "shorthand.1 One way is
shown below:
t0 V-36878:51 = 36874:S2-36875:S3 = 36876:S4 -36877
Now if you want to turn on a particular speaker, or set volume, you
can use the abbreviations . . . like, for instance: I
20 POKEV.15
30 POKES2.200
40 FORX = 1TO1000:NEXT
50 POKEV.O
VICTIP
In line 10, we put all the commands on one line instead of five
lines because we want to demonstrate economical program
ming techniques. You can save memory and "crunch" longer
programs into less space if you put several commands on a
single line, with each command separated by a colon, as
shown.
96