Detectability Threshold for Combination Tones

Experiments were performed on the detectability threshold for combination tones, defined as the sensation level of primary tones for which combination tones become audible. Investigated were (1) detectability threshold for h−l with (h−l)<<(h+l), where h and l are the frequencies of the higher and lower primary tone, respectively; (2) detectability threshold for 200, 400, and 600 cps with 800+1000 and 800+1400 cps as primary tones; (3) audibility of combination tones for l = 1000 cps and h variable between 1000 and 3000 cps; (4) detectability threshold for the “missing fundamental” of ${\displaystyle \sum _{\text{n−2}}^{10}}\hspace{0.17em}\cos \text{\hspace{0.17em}2\hspace{0.17em}πnft}$ , with f varying from 125 to 1000 cps. From the experimental data, we may conclude that (1) there are large individual differences in the minimum sensation level of primary tones for which combination tones appear; (2) for usual listening levels of speech and music, the ear's distortion is sufficiently low to avoid audible combination tones; (3) the same holds for the “missing fundamental,” so the fact that the pitch of a complex tone without fundamental is equal to the pitch of this tone cannot be explained by the assumption that the fundamental tone is reintroduced in the listener's ear; (4) the fact that the detectability thresholds for combination tones are significantly lower for small than for large tone intervals indicates that, for both cases, the ear's distortion cannot be represented by the same nonlinear characteristic and supports the evidence that the tones are produced in the inner ear.