Two pure tones fuse into a single rough tone below the critical bandwidth.

Evidence

These two pure tones are only perceived as separate pure tones when their frequency difference is greater than the critical bandwidth. Otherwise they are perceived as a single fused tone that is “rough” or as beats depending on the frequency difference between the two pure tones. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1570

These two pure tones are only perceived as separate pure tones when their frequency difference is greater than the critical bandwidth. Otherwise they are perceived as a single fused tone that is “rough” or as beats depending on the frequency difference between the two pure tones. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1570

Categorization

• DEFINE: Explains critical bandwidth as the threshold separating separate-tone perception from fused/rough perception.
• XREF: Connects to the discipline’s fusion/beats distinction, relevant to how dissonance and consonance are perceived.
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1570