scope:

This Recommendation¹ defines a single algorithm for assessing the speech quality of current and near future telephony systems that utilize a broad variety of coding, transport and speech enhancement technologies.

Based on the benchmark results presented within the studies of ITU-T, an overview of the test factors, coding technologies and applications to which this Recommendation applies is given in Tables 1 to 4. Table 1 presents factors and applications included in the requirement specification and which were used in the selection phase of the ITU-T P.863 algorithm. It should be noted that the performance of the ITU-T P.863 algorithm under each individual condition in Table 1 is not reflected in this table. Additional and detailed analysis will be undertaken in the characterization phase of the ITU-T P.863 algorithm. Table 2 presents a list of conditions for which this Recommendation is not intended to be used. Table 3 presents test variables for which further investigation is needed, or for which ITU-T P.863 is subject to claims of providing inaccurate predictions when used in conjunction with these. Finally, Table 4 lists factors, technologies and applications for which the ITU-T P.863 algorithm has not currently been validated. Note that the ITU-T P.863 algorithm cannot be used to replace subjective testing.

It should also be noted that the ITU-T P.863 algorithm does not provide a comprehensive evaluation of transmission quality. It only measures the effects of one-way speech distortion and noise on speech quality. The effects of delay, sidetone, echo, and other impairments related to two-way interaction (e.g., centre clipper) are not reflected in the ITU-T P.863 scores. Therefore, it is possible to have high ITU-T P.863 scores, yet poor overall conversational quality.

A characterization phase will follow the approval of this Recommendation. The purpose of the characterization phase is to prove the applicability of the ITU-T P.863 algorithm in real applications and may include new test conditions, new test scenarios and alternate test methodologies.

¹ This Recommendation includes an electronic attachment containing detailed descriptions in pdf format (see Annex B) and conformance testing data (see Annex A).