振幅変調音における包絡線の不規則変化の検知

概要

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The aim of this investigation was to determine the detection thresholds of sinusoidal and random changes in envelope of amplitude modulated (AM) signals. The envelope changes were obtained as a result of modulation of a pure-tone carrier by chosen types of modulators, which gave either sinusoidal, pseudorandom, or random (Gaussian) amplitude modulation. For pseudorandom and random modulation, the detection thresholds were determined when only modulation depth (m) of AM signals was changed randomly (f_m const) or when both modulation depth and modulation frequency (f_m) were changed randomly (f_m random). The data showed that for low modulation frequency (f_m≦64 Hz) the detection thresholds for sinusoidal amplitude modulation (SAM), pseudorandom amplitude modulation (PAM) and random amplitude modulation (RAM) overlapped one another in the limit of the standard deviation (SD). However, for higher modulation frequencies, the average threshold for the RAM (f_m const) was about 3 dB lower (around f_m=128 Hz) than that for sinusoidal amplitude modulation. In this case the PAM threshold was similar, within the limit of SD, to the SAM threshold. However, when random changes in amplitude were combimed with random changes in frequency, the PAM (f_m random), and RAM (f_m random) thresholds decreased about 5 dB relative to the SAM threshold.
社団法人日本音響学会の論文