Recommendation ITU-T P.863 describes an objective method for predicting overall listening speech quality from narrowband (NB) (300 to 3 400 Hz) to fullband (FB) (20 to 20 000 Hz) telecommunication scenarios as perceived by a user in an ITU-T P.800 or ITU-T P.830 absolute category rating (ACR) listening-only test. Recommendation ITU-T P.863 supports two operational modes, one for narrowband and one for fullband. Super-wideband (SWB) (50 to 14 000 Hz) experiments can be simulated by band limiting the reference and accordingly the degraded signal. This Recommendation presents a high-level description of the method and advice on how to use it. All essential parts of the model are described in detail, and are provided in separate pdf files (see Annex B). These files form an integral part of this Recommendation and shall take precedence in case of conflicts between the high-level descriptions included in the main body of this Recommendation and the corresponding detailed description parts. A conformance testing procedure is also specified in Annex A to allow a user to validate that an alternative implementation of the model is correct.

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

Edition 3 of ITU-T P.863 no longer applies an initial 14 kHz low-pass filter, therefore it is now able to consider spectral components above 14 kHz in its analysis. This expands the scope of application to fullband speech codecs (e.g., OPUS, enhanced voice service (EVS)). Additionally, the 'shift-jitter' which could be observed by repeated measurements with slightly differing delay, is decreased. The gain variation introduced by automatic gain control as well as slowly time-varying linear frequency distortions are now adequately considered.

Furthermore, the problems of ITU-T P.863 version 2 documented in the following implementer's guides were addressed and have been resolved:

former implementer's guide on assessment of EVS coded speech with Recommendation ITU‑T P.863 (2016);

former implementer's guide on non-validated test conditions with inserted gaps in speech by Recommendation ITU-T P.863 (2016);

former implementer's guide on discrimination of wideband (WB) and super-wideband speech by Recommendation ITU-T P.863 (2016);

former implementer's guide on correction of Recommendation ITU-T P.863 regarding reverb (2016).