On the Perception of Periodic Sound fluctuations (Roughness)

Psychoacoustic measurements of the roughness which is generated by amplitude- and frequency modulated tones, respectively, and by beating tone pairs reveal the following principles. (1) The physical parameter which almost exclusively determines roughness is the relative amplitude fluctuation (relative fluctuation of temporal envelope) which is present within frequency regions with the width of critical bands. The effect of the sound pressure level (i. e., of the absolute amplitude fluctuations) upon roughness is negligible. (2) The sensibility of the ear for the fluctuations decreases with increasing fluctuation frequency. This can be described by the low-pass characteristic of a simple R C-network with a timeconstant of about 13 ms. (3) The roughness of a sound whose spectrum covers several critical bands can be regarded as a sensation which is composed of the contributions of separate critical bands.

Investigations of the roughness of periodic pulse trains and of pairs of amplitude modulated tones confirm these results. Some conclusions concerning the roughness of musical sounds are drawn.