Roughness only emerges beyond 50 Hz frequency deviation then scales logarithmically

Evidence

The results displayed in Fig. 11.5 indicate that for frequency deviations up to 50 Hz only negligible values of roughness show up. For larger values of the frequency deviation L11 roughness increases almost linearly with the logarithm of L11. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1458

Categorization

• CANDY: A clean, quotable perceptual threshold: FM roughness is dead below 50 Hz deviation, then climbs with log frequency deviation.