On the number of channels needed to understand speech

Philipos C. Loizou, Michael Dorman, Zhemin Tu

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    148 Scopus citations


    Recent studies have shown that high levels of speech understanding could be achieved when the speech spectrum was divided into four channels and then reconstructed as a sum of four noise bands or sine waves with frequencies equal to the center frequencies of the channels. In these studies speech understanding was assessed using sentences produced by a single male talker. The aim of experiment 1 was to assess the number of channels necessary for a high level of speech understanding when sentences were produced by multiple talkers. In experiment 1, sentences produced by 135 different talkers were processed through n (2≤n≤16) number of channels, synthesized as a sum of n sinc waves with frequencies equal to the center frequencies of the filters, and presented to normal-hearing listeners for identification. A minimum of five channels was needed to achieve a high level (90%) of speech understanding. Asymptotic performance was achieved with eight channels, at least for the speech material used in this study. The outcome of experiment 1 demonstrated that the number of channels needed to reach asymptotic performance varies as a function of the recognition task and/or need for listeners to attend to fine phonetic detail. In experiment 2, sentences were processed through 6 and 16 channels and quantized into a small number of steps. The purpose of this experiment was to investigate whether listeners use across-channel differences in amplitude to code frequency information, particularly when speech is processed through a small number of channels. For sentences processed through six channels there was a significant reduction in speech understanding when the spectral amplitudes were quantized into a small number (<8) of steps. High levels (92%) of speech understanding were maintained for sentences processed through 16 channels and quantized into only 2 steps. The findings of experiment 2 suggest an inverse: relationship between the importance of spectral amplitude resolution (number of steps) and spectral resolution (number of channels).

    Original languageEnglish (US)
    Pages (from-to)2097-2103
    Number of pages7
    JournalJournal of the Acoustical Society of America
    Issue number4 I
    StatePublished - Jan 1 1999


    ASJC Scopus subject areas

    • Arts and Humanities (miscellaneous)
    • Acoustics and Ultrasonics

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