Two simultaneous tones generate audible lower tones absent from the stimulus

Evidence

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

When two pure tones are heard together, other tones with frequen­ cies 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 which is usually quite easily perceived is the difference (higher minus the lower) between the fre­ quencies of the two tones; this is known as the “difference tone”: where frequency of the difference tone frequency of t   he higher frequency pure tone and frequency of the lowe lf  r frequency pure tone Notice that this is the beat frequency when the frequency difference is less than approximately 12. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1611

Categorization

• DEFINE: Defines combination tones and difference tones, core psychoacoustic terminology.
• XREF: These phantom tones underpin how the ear reconstructs missing fundamentals, an idea explored later in the chapter. — connects to: Combination tones arise from the hearing system’s own nonlinearity — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 430; Combination tones become audible only above roughly 70 dB primary level; The ear generates audible combination tones not present in the stimulus — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1571 (+9 more)
• CANDY: The ear creates sounds that aren’t in the signal, a striking fact for casual conversation.
• QUESTION: What physiological mechanism generates these phantom lower tones? Worth chasing the nonlinear-cochlea explanation.
• corroborated: 3 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1571; David Howard, Jamie Angus, coustics and Psychoacoustics, 1611

Broader Connections

• Combination tones exist below both source tones and vary in audibility #corroborates (1.00)
• The ear generates phantom low tones absent from the actual signal #corroborates (0.92)
• A combined waveform can produce a perceived pitch absent from its actual frequency components #expands (0.85) — Eric J. Heller, Why You Hear What You Hear- An…, 323