Commodore Amiga A1000, Hardware Reference Manual

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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 on
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
production 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, readjust
the parameters and play it again, and so on.
The following works are recommended for more information on creating music with
computers:
o Wayne A. Bateman, Introduction to Computer Music (New York: John Wiley and Sons,
1980).
o Hal Chamberlain, Musical Applicators of Microprocessors (Rochelle Park, New Jersey:
Hayden, 1980).
INTRODUCING SOUND GENERATION
Sound travels through air to your ear drums as a repeated cycle of air pressure variations,
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, or timbre. Figure 5-1 shows a particular kind of waveform, called a sine
wave, that represents one cycle of a simple tone.
- 130 Audio Hardware -