title: On the number of channels needed to understand speech.
abstract: 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 < or = n < or = 16) number of channels, synthesized as a sum of n sine 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).
authors.affiliation: Department of Electrical Engineering, University of Texas at Dallas, Richardson 75083-0688, USA. loizou@utdallas.edu
authors.forename: P C
authors.initials: PC
authors.lastname: Loizou
authors.forename: M
authors.initials: M
authors.lastname: Dorman
authors.forename: Z
authors.initials: Z
authors.lastname: Tu
mesh_terms: D000161:Acoustic Stimulation / Q000295:instrumentation*; D000328:Adult; D003071:Cognition / Q000502:physiology*; D004867:Equipment Design; D006801:Humans; D008297:Male; D008954:Models, Biological; D013067:Speech Perception / Q000502:physiology*