Combination Tones

tones that arise in a nonlinear acoustic system in the presence of two or more sine-wave sound oscillations. The frequency of combination tones is expressed as a sum (summation tone) or a difference (difference tone) of the primary tones. The combination tones that arise in the human hearing apparatus when it is acted on by a high-intensity sound are called subjective tones (“Tartini tones”). The reason for the formation of such tones is the nonlinearity of the process of sound perception and of the mechanical system of the hearing apparatus. Differential subjective combination tones are of particular importance; because of these tones louder sounds appear to be richer in lower tones. Combination tones arising outside the human ear are called objective; such tones can arise because of nonlinearity of the sound source itself or of the sound-conducting medium. Combination tones are of great significance for the theory of musical instruments; they are also used in studying nonlinear distortions in acoustical apparatus.