Commodore VIC-20 User Manual page 242

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The VIC 20 User Guide
TABLE
7·1, Sound Register Memory Locations
Memory Location
36874
36875
36876
36877
36878
Volume Control Register
Sound Register
Low tone register
Middle range tone register
High tone register
Noise register
Volume control register
Memory location 36878 controls the volume of the sounds produced by
the VIC. Sixteen different volume levels can be selected. These range from 0
(off) to 15 (loudest). To control the volume, enter any value between 1 and
15. By itself, however, the volume control register produces no sound. You
also need the tone registers.
Tone Registers
The three tone registers (memory locations 36874, 36875, and 36876)
cover a frequency range of nearly nine musical octaves. These octaves are
not precise in terms of a standard musical scale because the frequencies
generated by the VIC 20's system clock are based on the computing
requirements of the microprocessor. For example, the VIC uses a frequency
of 443.888Hz as the note A.
Table 7-2 shows the frequencies covered by the VIC tone registers and
the approximate musical notes achieved, as well as the values you must
POKE into the tone registers to generate the frequencies.
POKEING A TONE
The lowest note the VIC 20 can produce is a low B (approximately 31
Hz, or 31 cycles per second). Enter the value for the lowest note into the low
tone register
POKE
36874
1
128
and turn on the maximum volume.
POKE
3687811~