Hearing resolves close tones through beats, rough fusion, then separation bands

Evidence

For the majority of listeners, beats are usually heard when the frequency difference between the tones is less than about 12.5 Hz, and the sensation of beats generally gives way to one of a “fused” tone that sounds “rough” when the frequency difference is increased above 15 Hz. As the frequency difference is increased further, there is a point at which the fused tone gives way to two separate tones but still with the sensation of roughness, and a further increase in frequency difference is needed for the rough sensation to become smooth. The smooth separate sensation persists while the two tones remain within the frequency range of the listener’s hearing. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 575 (#corroborates, via linked claim)

Categorization

• XREF: connects to: Clashing tones within one critical band produce roughness that underlies dissonance; Frequency separation between two tones systematically shifts fusion, roughness, then resolution; Perception of two tones progresses from beats to roughness to smoothness — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 575 (+6 more)

Broader Connections

• Perception of two tones progresses from beats to roughness to smoothness #corroborates (0.92) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 575
• Only harmonics separated by more than the ear’s critical bandwidth are resolved #qualifies (0.80)
• The ear switches from place to temporal pitch coding when harmonics stop being resolved #expands (0.78)
• Noise-induced hearing loss can unmask audible difference tones #expands (0.75)