of Microprocessors

MUSIC SYNTHESIS PRINOPLES 11
represent zero air pressure but instead represents zero variation from current
atmospheric pressure. Since only relatively rapid variations in pressure can be
heard, the baseline is usually taken as a zero reference and the positive and
negative variation around zero is the quantity of interest.
Even using an oscilloscope presents some problems. One of these is that
the screen is not very wide so only very short segments of the waveform may
be conveniently displayed. The best way to visualize a waveform is to have a
computer record it and display it on a graphic display or plot it on paper.
From now on when the term "sound" or "vibration" is used, it is assumed to
exist as an electrical signal. Listening to the sound is simply a matter of
feeding the signal to a high-fidelity amplifier and quality speaker system.
Typical Sound Waveforms
Figure 1-2 shows some typical waveforms of steady sounds. The horizontal
axis represents the passage of time and is marked off in milliseconds.
The vertical axis represents air pressure but is marked off in volts due to the
fact that the picture is actually of an electrical signal. The progression from
left to right is from the simplest possible pitched sound (sine wave) through
more complex pitched sounds to semipitched sounds a,od finally to the most
fundamental unpitched sound (white noise).
The waveforms in Figs. 1-2A and B are from unquestionably pitched
sounds. Their distinguishing feature is that the waveform repeats itself
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