Manx SJ-2, Руководство пользователя

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8
Frequency and Waveforms...................a little bit of magic!
It just so happens that sound waves don’t like to propagate through air in any form other than a sine
wave.
It stands to reason; air which is of a higher pressure because of a sound wave will want to expand
quickly, but this urgency will dampen off as the pressure returns to normal, and a subsequent rebound in
the other direction will complete a sign wave pattern. Similar physics are at work in a swinging pendulum
- it will only prescribe a sine wave pattern.
However, we can clearly hear square or sawtooth shaped waves coming out of a synthesizer. And,
although they don’t commonly occur in nature, you can hear these waves coming off of electrical
installations and other machinery as well. How is this so?
The answer lies in adding sine waves together - in other words, hearing more than one sine wave
at the same time. Consider the diagram below, which graphically illustrates hearing a loud low pitched
sine wave, and a much quieter high pitched sine wave, both at the same time:
If that appears to be intuitive, this instance may not. Look what happens when we decrease the
gap between the high and low sine waves, so now they are of a similar but not identical pitch:
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24 Appendix One - Audio filters