of Microprocessors

30 MUSICAL ApPUCATIONS OF MICROPROCESSORS
absence of a repeating wave pattern is rather academic, but it will be important
later.
Unpitched sounds and most semipitched sounds are like the waveforms
of Fig. i-2D and E-real messes that look more like an infant's scribbling.
Time waveforms of such sounds give almost no clues about how they will
sound. A spectrum plOt, however, will reveal quite a bit. The first obvious
feature is that there is a very large number of lines representing component
sine waves. With such a large number, the spectral envelope takes on added
significance. In fact, most sounds of this type literally have an infinite
number of component frequencies so the envelope is all that can be really
plotted.
The spectrum in Fig. i-3D is special. It is nothing more than a
straight line! Such a sound is called white noise because it has an even mixture
of all audible frequencies. This is analogous to white light, which is an evenmixture
of all visible light frequencies. Any departure from a straight spectral
plot can be called coloring the sound, analogous to coloring light by
making one group of frequencies stronger than others.
Pure white noise sounds like rushing air or distant surf. If the lower
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0.2
2 3 4 5 6 7
FREQUENCY (Hz 1100)
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FREQUENCY (Hz 1100)
(D)
Fig. 1-8. Spectrum plot (cant.). (C) Waveform of Fig. 1-20. (D) Waveform of
Fig. 1-2E.