VoIP Voice and Fax Signal Processing

20.1 VOICE QUALITY MEASUREMENTS

For comparing the voice quality, and to arrive at the parameters contributing to the voice quality, it is required to know how voice quality is measured and what are the quality goals. The basic test setup for VoIP voice measurements is given in Chapter 13. In this chapter, voice quality as mean opinion scores (MOS), various classifications, voice quality influencing parameters, and improvements are discussed. Voice quality measurements for MOS are classified as subjective and objective.

A functional representation of some popular voice quality measurement techniques is illustrated in Fig. 20.1. In the figure, voice is shown to be from the sending gateway to the receiving gateway. The receiving gateway is shown with some more expanded blocks for creating a big picture of the E-model, which is used for R-factor estimation, additional quality metrics, and Real-Time Transport Control Protocol-Extended Reports (RTCP-XR) operation. In the E-model, RTP, RTCP, jitter buffer, and total system signal parameters are used. When on calculating the R-factor and other derived parameters, RTCP-XR can send packets to the internal applications, destination gateway, and RTCP-XR server. In summary, the nonintrusive R-factor is an objective estimation that resides as part of VoIP implementation, and additional software is required in the gateway for the R-factor estimation. In perceptual evaluation of speech quality (PESQ), instruments like MultiDSLA [URL (DSLAII)] ...