Speech quality assessment of compounded digital telecommunication systems; perceptual dimensions

Digital telecommunication networks may involve a multiple number of public switched telephone networks (PSTN), cellular and mobile systems and to some extent also satellite systems. Most of these networks contain non-linear speech coders and other speech algorithms which may degrade the overall end-to-end quality of speech. An important problem is how to assess the speech quality of such compounded systems. The object of this paper is to describe the first stage of the construction of a proposed three-layer model for speech quality assessment. A subjective test of the speech quality of 16 different compounded transmission paths (mixtures of PCM, GSM full and half rate, DECT, CELP, LD CELP, FS10-16) is carried out by 40 subjects using 21 different rating scales. The main result of this paper is the test results which lead to the definition of four main perceptual dimensions to be used in the second layer of the proposed model