Abstract
The detection threshold for frequency modulation was measured at several carrier frequencies. The standard (unmodulated) waveform was a sinusoidal signal of fixed amplitude and fixed frequency. The comparison waveform was frequency modulated. The modulating signal had constant frequency, but the amplitude was a random variable. The amplitude of each successive period was the absolute value of a Gaussian random variable with mean, 0, and standard deviation, σ. The ability of listeners to detect the FM modulation by adaptively varying σ in a two‐alternative forced‐choice procedure was determined. An increase in the carrier frequency from 120 to 1000 Hz causes, on average, a three‐fold increase in the threshold value of σ. Changes in modulation frequencies from 4 to 16 Hz increase the threshold by twofold at the highest carrier frequency. At low‐modulation frequencies, different amplitude samples produce statistically different discrimination thresholds. Compared with the classical data for FM signals, the random deviations are easier to hear at higher carrier frequencies and harder to hear at lower carrier frequencies. [Research supported by the Kosciuszko Foundation and the NIH.]
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