Combination tones arise from the hearing system’s own nonlinearity

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

Categorization

• DEFINE: Clarifies that audible difference tones near 600 Hz arise from nonlinear distortion inside the listener’s own auditory system, not from the signals presented.
• XREF: Connects to combination-tone and distortion-product otoacoustic emission phenomena in later psychoacoustics and audiology literature. — connects to: Nonlinear cochlear mechanics make listeners perceive nonexistent difference tones; Combination tones exist below both source tones and vary in audibility; Cubic difference tones in hearing defy regular nonlinear transfer models (+15 more)
• corroborated: 2 independent passages support this claim — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 430

Broader Connections

• Nonlinear cochlear mechanics make listeners perceive nonexistent difference tones #corroborates (1.00)
• The ear generates audible combination tones not present in the stimulus #corroborates (0.95) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1571
• Two frequencies can mechanically generate sum and difference frequencies in the ear #corroborates (0.95)
• Difference noise generated by ear nonlinearities can be heard before the test tone itself #corroborates (0.90)
• Two simultaneous tones generate audible lower tones absent from the stimulus #corroborates (0.90) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1571
• Combination tones exist below both source tones and vary in audibility #expands (0.85)
• Human hearing is highly nonlinear and cannot be LTI-modelled beyond peripheral parts #corroborates (0.85)
• Nonlinear distortion generates new frequencies that change timbre with volume #expands (0.80)
• Combination tones can be objectively measured in the outer ear canal #expands (0.80)
• Cubic difference tones in hearing defy regular nonlinear transfer models #qualifies (0.75)