The peripheral auditory system functions like a frequency analyser, often modelled as a bank of non-overlapping band-pass filters called critical bands; 20 bands are necessary for simulating frequency resolution of the ear within an ordinary frequency range of speech (up to 7,000 Hz). A far smaller number of filters seemed sufficient, however, to re-synthesise intelligible speech sentences with power fluctuations of the speech signals passing through them; nevertheless, the number and frequency ranges of the frequency bands for efficient speech communication are yet unknown. We derived four common frequency bands - covering approximately 50-540, 540-1,700, 1,700-3,300, and above 3,300 Hz - from factor analyses of spectral fluctuations in eight different spoken languages/dialects. The analyses robustly led to three factors common to all languages investigated - the low &mid-high factor related to the two separate frequency ranges of 50-540 and 1,700-3,300 Hz, the mid-low factor the range of 540-1,700 Hz, and the high factor the range above 3,300 Hz - in these different languages/dialects, suggesting a language universal.
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