Evaluation of broad-band noise mixed with amplitudemodulated sounds

A series of experiments was conducted concerning the effect of amplitude-modulated (AM) sounds on the impression of broad-band noise. The following results were found:(1) AM sounds in broad-band noise were detected when S/N was around zero (S: the level of AM sound, N: 1/3 octave band level of broad-band noise with center frequency corresponding to the carrier frequency of AM sounds). Close examination showed that carrier frequency, modulation frequency and modulation depth had a systematic effect on the detection of AM sounds.(2) The loudness of broad-band noise mixed with AM sounds could be approximately evaluated by loudness level based on ISO 532B (LLz).(3) The timbre of broad-band noise mixed with AM sounds was judged to be more metallic as the carrier frequency of AM sounds became higher and to be more clamorous as the carrier frequency became lower. This suggests that the timbre is deteriorated when AM sounds are mixed with broad-band noise. The three factors were extracted by the factor analysis: they were “metallic” or “unpleasant, ” “powerful” and “rough.”