Commodore VIC-20 - Pure Tones

Chapter 7: Sound 233
THE COMPONENTS OF SOUND
Pure Tones
The tone registers at memory locations 36874, 36875, and 36876 pro-
duce continuous frequencies ranging from
about 31 Hz (cycles per second)
to 15,980 Hz. A cycle, in tonal frequencies, refers to a sound
that starts at its
minimum volume, rises to its maximum volume,
and falls again to its
minimum volume.
j
o
>~~------~----~----~
Minimum volume
The actual tone of a sound is a direct function of its frequency (how
quickly it rises and falls).
If you double the frequency, you will have a tone
exactly one octave higher
than before. Try this program.
10 POKE 36878,15
20 GET A$: IF A$ • '"' THEN 20
30 IF Af • CHRf(133) THEN 70
40 IF A$ • CHR$(134) THEN 88
50 IF A$ • CHRf(135) THEN 90
60 IF AS • CHR$(136) THEN 100
65 GOTO 20
70 POKE 36876,0: POKE 36875,0: POKE 36874,240: ooro 28
80 POKE 36876,0: POKE 36874,0: POKE 36875,240: ooro 20
99 POKE 36875,O: POKE 36874,0: POKE 36876,248: OOTO 20
100 IF PEEK(36878) a 9 THEN 10
110 POKE 36878,O: GOTO 29
Line 10 turns on the volume control register so you will be able to hear
the sounds produced by the tone registers. Line
20 waits for a keystroke. If
the FI key is pressed, 0 is POKEd into the middle and high tone registers and
208 is POKEd into the low tone register. Pressing the F3 key POKEs 0 into
the high
and low tone registers and 208 into the middle tone register.