Detecting single-cycle frequency modulation imposed on sinusoidal, harmonic, and inharmonic carriers

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Abstract
Thresholds for detecting frequency modulation(FM) of various carriers were measured in quiet and in noise. The carriers were either pure tones, harmonic complexes, or inharmonic complexes. The modulator was always a single cycle of a 12.5‐Hz sinusoid. When the carrier was a complex tone, each component of that carrier was modulated by the same percentage of its starting frequency. This is the form of FM that occurs when the fundamental frequency (F0) of a complex sound is modulated. Threshold was defined in terms of this percentage frequency change. Two phases of the modulator were used, producing percepts of either upward or downward frequency glides. Experiment 1 used sinusoidal carriers with frequencies between 200 and 2400 Hz. Thresholds were constant for carrier frequencies of 1200 Hz and above, increased below 800 Hz, and were higher for the ‘‘down’’ than for the ‘‘up’’ glides, especially with low carrier frequencies. Experiment 2 measured thresholds for carriers consisting of three adjacent harmonics of complexes with F0’s of 50, 100, and 200 Hz as a function of the frequency of the center component of each complex (CF). Thresholds varied with CF in a similar way to those for the pure‐tone carriers. In the frequency region 1200–2400 Hz, where thresholds did not vary with CF, they did not vary systematically with F0. Experiment 3 compared thresholds for a 20‐component harmonic complex with those for an inharmonic complex. Thresholds were only slightly lower for the harmonic complex than for the inharmonic complex when presented in quiet, but were much lower when the complexes were presented in bursts of pink noise. Thresholds in noise for the completely harmonic complex were also lower than those for 20‐component complexes in which only five adjacent components shared a harmonic relationship. It was concluded that a harmonic relationship between components occupying widely different frequency regions aids the detection of frequency modulation, particularly in the presence of noise.

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