The Channel Capacity of the Ear as a Function of Frequency

Abstract

The channel capacity of the ear as a function of frequency can be computed by a technique similar to that in an earlier paper [E. L. R. Corliss, J. Acoust. Soc. Amer. 50, 671–677 (1971)]. The legitimacy of this computation rests upon the justification that sufficient variables are involved to permit replacement of actual statistical distributions by normal distributions. This legitimacy is tested by comparing the predicted growth of intelligibility of individual phonemes as a function of level above threshold with experimental results. The channel capacity of the ear shows a broad maximum in the frequency range of 3–6 kHz. Taking into account the duration of speech sounds as a function of frequency, one finds that each phoneme tends to convey the same number of bits over the range from 300 Hz to 4 kHz. However, many more phonemes are uttered per unit time at the higher frequencies, so that the rate of information transfer is higher. This explains to some extent the empirical observation that the high-frequency limit necessary for accurate communication depends upon redundancy of the material. One ought to reconsider the convention that the spectrum above 3 kHz is relatively irrelevant for speech communication when unfamiliar speech material must be recognized.