When two pure tones are sounded, a lower note of frequency equal to the difference of the frequencies of the two individual notes may be heard. This is the simple difference tone (also sometimes called the ‘Tartini tone’). It is usually ascribed to non-linearities in the audio system producing the sounds or to non-linearities in the hearing mechanism, and is one of the combination tones with frequency f2–f1. Another combination tone with frequency 2f1–f2, is also sometimes heard; this is the cubic difference tone. Difference tones are most frequently audible in a musical context when two instruments, e.g. flutes, are played together in the high register. See also Sound and Combination tone.
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