Only about twenty audible roughness steps span the entire perceptual range

Evidence

An increment of roughness becomes audible for an increment in the degree of modulation of about 10%, which corresponds to an increment of about 17% in roughness. For amplitude-modulated I-kHz tones and a modulation frequency of 70 Hz, a threshold of roughness is reached for values close to 0.07 asper. One asper is close to the maximum roughness for amplitude-modulated tones; there are thus only about 20 audible roughness steps throughout the total range of roughnesses. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1453

Categorization

• DEFINE: Introduces the asper as the unit of roughness and the threshold of 0.07 asper.
• corroborated: 2 independent passages support this claim — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1453