Perception of two tones progresses from beats to roughness to smoothness
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
Categorization
- QUESTION: Why 12.5-15 Hz specifically — what anatomical or neural mechanisms set that boundary between fused roughness and separate tones?
- corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 575
- XREF: connects to: Low modulation frequencies produce fluctuation sensation while higher ones produce roughness — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1381; Roughness grows faster with modulation depth for tones than for noise; Sensory consonance depends on roughness, sharpness, and tonalness — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 2040 (+6 more)