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