Objective speech quality assessment of compounded digital telecommunication systems

Digital telecommunication networks involve 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 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 development of a proposed three-layer model for objective speech quality assessment. The design of the objective measure is based on a subjective test of the speech quality of 16 compounded transmission paths and involves 40 subjects using 21 different rating scales. The subjective test supports the definition of four main perceptual dimensions to be used in the second layer of the proposed model. These defined perceptual elements form the basis of designing an objective measure for predicting the total quality of a given telecommunication connection.