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Bob UK
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Posted on Tuesday, 16 December, 2014 - 08:05:   Edit PostDelete PostView Post/Check IP

In another thread about engine cooling fans the word heterodyne turned up. Which I called beating. Heterodyne is where two frequencies produce a third frequency. If a musical frequency of say 440Hz is played with a frequency of 444 Hz then a third frequency of 4 Hz will also be heard. Because 4 Hz is low it sounds as a beat. A piano tuner uses the beats to tune a piano and I use them to tune stringed instruments, the slower the beat the closer I getting to the required pitch.

Note that pitch and frequency aren't the same thing, pitch is what we hear and frequency is the science measurement. Ears work from 20 Hz to 20k Hz. Low sounds sound higher than they actually are and high sounds lower. The tuner stretches the notes to make it sound right, and that is the hard part of piano tuning.

Apply the above to a fan that is moving air. Sound is moving air.

This also applys to light and electronics or anything that has frequency.

(Message approved by david_gore)