Roughness depends on modulation degree or FM index plus modulation rate

Evidence

This dependence of roughness on the degree of modulation holds for tones of other centre frequencies also, although the modulation frequency at which the maximum roughness is reached depends on centre frequency. Figure 11.2 shows the dependence of roughness on modulation frequency at different centre frequencies for 100% modulation. This dependence has a band-pass characteristic. Roughness increases almost linearly from low modulation frequencies, in the double-logarithmic coordinates of Fig. 11.2, before it reaches a maximum. The maximum only depends on carrier frequency below 1 kHz where the maximum is shifted towards lower frequency of modulation with decreasing carrier frequency. The lower slope of this band-pass characteristic remains the same for frequencies of modulation below 1 kHz, even though the maximum decreases with decreasing centre frequency. For centre frequencies above 1 kHz, the height of the maximum is reduced although the frequency of modulation at which this maximum is reached remains unchanged. This means that above I-kHz centre frequency there is a parallel shift downwards of the characteristic with increa’iing centre frequency. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1440

For amplitude modulation, the important parameters are the degree of modulation and modulation frequency. For frequency modulation, it is the frequency modulation index and modulation frequency. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1436

The dependency of roughness on the degree of modulation is demonstrated. You will hear an amplitude modulated 1 kHz tone with a modulation frequency of 70 Hz and a varying degree of modulation of 1.0, 0.7, 0.4, 0.25, 0.125, 0.1, and O. The roughness of the sound will decrease with smaller degrees of modulation. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 3341

Categorization

• DEFINE: Two-parameter characterization: amplitude modulation uses degree of modulation, frequency modulation uses the FM index.
• corroborated: 3 independent passages support this claim — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1440; Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1436; Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 3341