Combination tones beat against other near-pitched instruments unless masked

Evidence

At test-tone frequencies near 1.4 kHz, the subject indicates audibility of an additional tone at the relatively low test-tone level of 40 dB. A careful examination of these results and discussions with experienced subjects show that inexperienced subjects do not hear the test tone at that frequency and level, but a difference tone near 600 Hz. This difference tone is produced through nonlinear distortions that originate in our own hearing system. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 430 (#expands, via linked claim)

When two pure tones are heard together, other tones with frequencies lower than the frequencies of either of the two pure tones themselves may be heard also. These lower tones are not acoustically present in the stimulating signal, and they occur as a result of the stimulus consisting of a “combination” of at least two pure tones; they are known as “combination tones.” … The frequency of one such combination tone that is usually quite easily perceived is the difference (higher minus the lower) between the frequencies of the two tones; this is known as the “difference tone”: where fd = frequency of the difference tone fh = frequency of the higher-frequency pure tone and fl = frequency of the lower-frequency pure tone Notice that this is the beat frequency when the frequency difference is less than approximately 12. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1571 (#expands, via linked claim)

Categorization

• XREF: connects to: Pure-tone instruments readily produce audible combination tones — David Howard, Jamie Angus, coustics and Psychoacoustics, 1621; Combination tones exist below both source tones and vary in audibility; Upward masking makes intermodulation difference tones more audible than harmonics — Toole, Floyd E, Sound reproduction- the acoustics and…, 989 (+2 more)

Broader Connections

• Combination tones exist below both source tones and vary in audibility #expands (0.85)
• Combination tones arise from the hearing system’s own nonlinearity #expands (0.82) — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 430
• The ear generates audible combination tones not present in the stimulus #expands (0.80) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1571
• Upward masking makes intermodulation difference tones more audible than harmonics #qualifies (0.72) — Toole, Floyd E, Sound reproduction- the acoustics and…, 989