The application of the Speech Transmission Index (STI) method to testing digital transmission channels

An objective method of measuring the quality of speech transmission channels with respect to intelligibility was applied to digital channels in order to test whether the specific distortions present on such channels are accounted for correctly by the STI. The STI and PB word intelligibility were measured for a great number of PCM and delta modulation channels. Results show that the relation between STI and PB word intelligibility does not differ significantly from the results found in the case of analog channels.