Difference tone
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Difference tone is a bio-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.
It is the consequence of non-linear distortion of the response of the human ear. It appears that mainly the inner ear non-linearity produces this distortion, while the middle ear response is quite linear at normal sound levels.
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.
External links
- Hearing Sounds (http://www.isvr.soton.ac.uk/SPCG/Tutorial/Tutorial/Tutorial_files/Web-hearing-difference.htm)