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t.pps #44
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2022-08-26
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======================================
PEEKs, POKEs, & SYSes, Part 44
by Jim Weiler and Reggie Beavers
======================================
Ok, all you audiophiles, listen up!
This month we will finally learn
enough to make some music. Let's
see, you learned about ADSR two
months ago and waveform last month...
I guess you're old enough now to
learn about pitch.
-------
PITCH
-------
At last we've reached a topic we
can relate directly and exactly to
something in the real world. Pitch
refers to the... er... pitch of a
note. That is, the voice of a
screaming thrush is high-pitched, and
a foghorn is low-pitched.
In technical terms, pitch is
frequency. High pitch = high
frequency. In musical terms, pitch
is the note you play. High pitch =
high (trebel) note. In medical
terms, pitch relates inversely to
temperature. The lower the
temperature of the stethoscope, the
higher the pitch of the scream.
Each SID voice has its own pitch
registers, so each voice can have its
own pitch. That means you can use
the three voices to play chords or
three-part harmony (or discords if
that's what you want).
If S=54272, then you set the pitch
for voice one by poking values into
S+0 and S+1. What values? That
depends entirely on what pitch you
want. You can choose any of 65536
values. Values near zero are so bass
that they don't even seem to have
pitch - just a bunch of clicks.
Values above 256 fall in what is
generally considered the "musical"
range.
But not all pitches are musical
notes. That is, not all of the 65536
pitches correspond to keys on a piano
keyboard. In fact, only about 123 of
the 65536 pitches available to SID
are musical notes. Which 123? Well,
you'll just have to read on for that
information. We supply you with a
chart somewhere in this month's
PEEKs, POKEs, and SYSes.
----< continued in next article >----