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Open Access Evaluation of Speech Transmission Channels by Using Artificial Signals

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A method is presented by which the effect of some current types of interferences on speech intelligibility can be quantified on the basis of simple physical measurements. The approach is based on the relationship of perceptual differences and physical differences among speech sounds. This relationship suggests that the effect of a transmission channel on intelligibility is strongly related to the degree to which the spectral differences, originated at the talker side, are preserved at the listener side. This leads to the definition of the Speech Transmission Index (STI) based upon: (1) a simple artificial test signal by which a “standard” spectral difference is introduced at the talker side of the channel, and (2) an analyzing procedure to be applied to the test signal received at the listener side in order to quantify the degree of preservation of the spectral difference introduced. The test signal and the analyzing procedure are optimized on the basis of the rank-order correlation between the STI-values and PB-word scores obtained for 50 different transmission channels, subjected to peak clipping, band-pass limiting, interfering noise or reverberation, in various degrees and a number of combinations. The relation between the STI approach and other methods is discussed.

Document Type: Research Article

Publication date: December 1, 1971

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