An acoustic key to eight languages/dialects: Factor analyses of critical-band-filtered speech

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.