Comodulation across bands had no effect so it appears that sidebands providing a denser spectrum improved performance. Experiment 3 tested the relative contributions of comodulation across bands and spectral density to improved performance with a sine carrier and high cutoff.
A low cutoff led to poorest performance, regardless of carrier. A noise carrier combined with a high cutoff allowed intonation to be perceived to some degree but performance was best in high-cutoff sine conditions. Experiment 2 measured perceptibility of cues to voice pitch variations. With a high cutoff, performance was better for sine-vocoding. With a low cutoff, performance was better for noise-vocoding than for sine-vocoding. Performance was better with a high cutoff for sine-vocoding, with no effect of cutoff for noise-vocoding. Experiment 1 varied envelope cutoff frequency (30 and 300 Hz), carrier type (sine and noise), and number of bands (2–5) for vocoded speech presented to normal-hearing listeners. The choice of processing parameters for vocoded signals may have an important effect on the availability of various auditory features.
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