Difference tone

Difference tone is a psycho-acoustic phenomenon. When two tones are played simultaneously, a hearer can in addition perceive the tone whose frequency is a sum or difference of the two frequencies. The discovery of the phenomenon is credited to the violinist Giuseppe Tartini.

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For a long time it was thought the consequence of non-linear distortion of the response of the human ear. The inner ear's non-linearity should be responsible for this distortion, while the middle ear response is quite linear at normal sound levels.

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If two pure tones of frequencies f1 and f2 are present in a sound, the ear non-linearity would produce intermodulation tones of frequencies equal to the sums and differences of whole multiples of the two frequencies. In particular, a difference tone of 2f1 − f2 is quite pronounced for certain choices of frequencies.

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An experiment using headphones providing two different frequencies to each ear would however still lead to perception of difference tones, hence falsificating the theory that non-linear distortion was the responsible factor.

Related Topics:
Headphones - Perception - Falsificating - Theory - Non-linear distortion

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