228
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~
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