o
How
to
use
the audio channels for special effects, wiring them for stereo sound if
desired, or using one channel to modulate another.
o
How
to
produce quality sound within the system limitations.
A section
at
the end of the chapter gives you values
to
use for creating musical notes
OR
the equal-tempered musical scale.
This chapter is not a tutorial on computer sound synthesis; a thorough description of
creating sound on a computer would require a far longer document.
The
purpose here
is
to
point the way and show you
how
to use the Amiga's features. Computer sound pro-
duction is fun
but
complex, and it usually requires a great deal of trial and error on the
part
of the
user-you
use
the instructions to create some sound and play it back, read-
just
the parameters and play
it
again, and so on.
The
following works are recommended for more information on creating music with com-
puters:
o Wayne
A.
Bateman, Introduction to Oomputer }'lusic (New York: John Wiley
and Sons, 1980).
o Hal Chamberlain,
}'lusical Applications
of
}'licroprocessors (Rochelle Park, New
Jersey: Hayden, 1980).
INTRODUCING
SOUND
GENERATION
Sound travels through air to your ear drums as a repeated cycle of air pressure varia-
tions,
or
sound waves. Sounds can be represented as graphs
that
model how the air
pressure varies over time.
The
attributes of a sound, as you hear it, are related
to
the
shape of the graph. If the waveform is regular and repetitive,
it
will sound like a tone
with steady pitch (highness or lowness), such as a single musical note. Each repetition of
a waveform is called a cycle of the sound.
If
the waveform
is
irregular, the sound will
have little or no pitch, like a loud clash or rushing water. How often the waveform
repeats (its frequency) has an effect upon its pitch; sounds with higher frequencies are
higher in pitch. Humans can hear sounds
that
have a frequency of between
20
and
20,000 cycles per second.
The
amplitude of the waveform (highest point on the graph),
is related to the perceived loudness of the sound. Finally, the general shape of the
waveform determines its tone quality,
0)'
timbre. Figure
5-1
shows a particular kind of
waveform, called a sine wave,
that
represents one cycle of a simple tone.
132
Audio Hardware
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