International Standardization International Standardization of perceptual audio measurement techniques was mainly driven by two expert groups within the International Telecommunications Union (ITU).

> ITU-T P.861 "PSQM" Within the telecommunication sector of the ITU, in 1996 Study Group 12 finalized recommendation P.861 [ITUT861] for the objective analysis of speech codecs. After a wide-ranging comparison of proposed methods, the group opted for the PSQM algorithm of KPN Research. PSQM showed high correlation of up to 98 percent with the scores of subjective listening tests. PSQM was successfully introduced to the telecom market during the following years by OPTICOM.

> ITU-T P.862 "PESQ" Driven by the demand for a verified test procedure that could not only handle speech coding, but the whole end-to-end signal path, the expert group within ITU-T SG12 started working on an improved speech quality model. For instance varying delays and artefacts due to packet loss, such as encountered with VoIP, could not be assessed with the original PSQM method, as delay compensation was not provided for by the P.861 standard. Proprietary advancements of the standard, such as provided by KPN (PSQM+, PSQM99) and OPTICOM (PSQM/IP), could adapt PSQM well to the new range of artefacts. Nevertheless, a new standard was needed.

After a competitive development phase, the new model "PESQ" was devised. PESQ stands for "Perceptual Evaluation of Speech Quality". PESQ combines a further refinement of PSQM and "PAMS", a proprietary model devised by BT. Extensive tests showed PESQ's superior performance especially for VoIP applications. In February 2001, PESQ was accepted as the new state-of-the-art ITU-T Rec. P.862.

> ITU-R BS.1387 "PEAQ" Within the study period 1994 – 1998, the ITU-R had established task group 10/4 with the scope to recommend an objective, perception based model to evaluate the quality of wide-band audio codecs. After collecting a set of proposals, including the most popular ideas such as NMR, PAQM, PERCEVAL, POM and others, the group of model proponents, opted for a joint collaboration to derive an improved model. In 1998, two versions of this new model were presented: A 'Basic Version', featuring a low complexity approach, and an 'Advanced Version' for higher accuracy at the trade-off of higher complexity. After thorough verification, the model was recommended as a measure for the Perceptual Evaluation of Audio Quality 'PEAQ' under recommendation BS.1387 in late 1998 and revised in 2001.

This set of standards, ITU-T P.861, ITU-T P.862 and ITU-R BS.1387, marks the development of state-of-the-art techniques for the objective evaluation of the perceived quality of audio codecs. All these techniques were derived from modeling the corresponding subjective experiment by an algorithm based approach. Thus it is essential to understand the scope of the modeled subjective experiment, when trying to interpret the calculated results. The following diagram summarizes the subjective test procedures and their corresponding objective counterparts in the context of typical bit rate limits. As mentioned earlier, the threshold between both worlds – wide-band audio and telecommunication - is floating due to the steadily attempt to further reduce the bit rates by more efficient coding schemes. Consequently, the overall data rate scale depicted in the figure should be taken as a course indicator only.

Compare Standardized Subjective and Objective Analysis Methods
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