Atari XL

Sound and Music
128 + 32 + 8 + 4 + 2 + 1 = 175
97
You can achieve the same effects as those
obtainable with the SOUND command in this way,
but this knowledge isn't much use. But what about
bit 4 of the control register? This is the volume
only bit and when set to 1, the value of the volume
bits (0 to 3) is used to directly control the speaker of
the TV.
Bits 0 to 3 select a voltage which is applied to the
TV speaker if bit 4 is set. The higher the value of
bits 0 to 3, the higher the voltage and the greater
the deflection of the TV speaker.
For example type:
POKE 53763,31
When you press the RETURN key, you will hear
the beep as you press the key, followed by a click
from the speaker.
POKE 53763,16
will select a zero voltage and the speaker will
return to its rest position, with another click. This
is how the XL creates noises with square waves,
each pulse of which moves the speaker out then
back to rest again.
Type in the following program, which steadily
increases the voltage applied to the speaker.
10 FOR VOLTS=l TO 15
20 FOR Z=l TO 100
30 POKE 53763,16+VOLTS
40 POKE 53763,16:REM 0 VOLTS
50 NEXT Z
60 NEXT VOLTS