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Re: Difference tones

Author: Craig Matovich
Date: 2006-12-28 22:32

One way to understand difference tones is in consideration of where two different tones lie in the overtone series.

Consider C major... the fundamental is c.

Ask yourself where in the over tone series lies a major third? Counting up from the fundamental, the low c is 1, octave c is 2, next upper g (P5) is 3, next c (P4) 4, and finally 'e'. a major 3rd above its predecessor in the over tones series occurs. Count it as 5.

The ratio between 5 and 4 (c and e) produces a difference tone of 1.
(upper tone - lower tone = difference tone). Another way of saying that is the ratio of the (pitch of the upper note - pitch of lower note) produces a difference tone equal to the difference based on the ratio.

For pitches of 880 and 440 the difference tone = 220. If 880 is the 3rd in the series, and 440 is the 2nd, subtract the lower series element form the higher and the result identifies where the difference tone lies in the overtone series. In this case its the fundamantal or 1st series element.

Closer high note harmonies produce more noticible difference tones. If the difference tone is 'in tune' it reinforces the harmony.

Try this... set a loud tone on a tuner to a fairly high note on the 5th scale degree (perhaps use the oboe's 2nd octave g or b). Play the 3rd scale tone below the reference tone until the difference is apparent. It appears as kind of a buzz in your ear.

Then try playing the scale from tonic a 5th below the reference tone. Play slowly, hear the difference tone and then alter your pitch and listen as the difference tone moves around. The higher your pitch, the lower the difference tone and vice versa...

Its interesting stuff. Once attuned to it, you will hear some crazy stuff happening.

Post Edited (2006-12-30 03:08)

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