Musical Acoustics

What are difference tones?

Difference tones are frequencies that are produced as a result of two different frequencies mixing with each other. This mixing can only occur if a device is non-linear. That is, if the output is not a multiple of the input. You can create difference tones with two toy slide whistles. Place both in your mouth and blow hard. Adjust their lengths so that the two tones are the same pitch. Then adjust one. As you move its pitch away from the other you will hear a low-pitched sound whose pitch increases as the two whistles’ pitches get further apart. For example, if the high-frequency sound was 812 hertz, while the lower frequency was 756 hertz, the difference tone from the interfering sound waves would be 144 hertz. The non-linear device in this case is your ear!


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