SIST-V ETSI/EG 201 377-1 V1.3.2:2010 PDF

The present document is part 1 of a series of documents on the specification and measurement of mouth-to-ear (also end-to-end) speech transmission quality. Its main objective is to describe objective comparison-based methods and systems for measuring mouth-to-ear speech quality in networks. Apart from this, it gives an overview on other important aspects of mouth-to-ear speech quality. As the need arises, these other aspects will be covered in more detail in subsequent parts of the present document. Although some of the models described in the present document are superseded the description of the models is kept for information. The present document gives an overview of the methods available for measuring one-way speech transmission quality. Its purpose is to give information and guidance primarily for operators, users, consumer organizations and regulators who wish to measure or compare the speech transmission quality provided by different networks. The need for the present document has been increased by: the liberalization of voice services, which has introduced alternative competing providers of voice services; the introduction of new mobile and IP based technologies; which has increased the range of services and cost/quality options for users. The present document applies to both fixed and mobile networks with or without terminal equipment connected to the network. It applies only for narrowband (i.e. between 300 Hz and 3 400 Hz) communications. In principle, comparison methods can be used for IP-based (internet protocol-based) networks, but further work is needed on the calibration of the methods for such networks. The present document describes: methods for measurements of individual impairments or combinations of impairments to be made at acoustic or electrical interfaces; methods for combining measures of different impairments into a single objective measure; methods for predicting the subjective effect of impairments that would be perceived by users. The methods in the present document assume that subjects with normal hearing have been involved in the test. Therefore, the instrumental methods estimate the perceived speech quality of persons with normal hearing. For each method, the guide contains a general description to highlight the main points, and provides references for more detailed information. The present document does not contain detailed specifications of the individual methods. The present document concentrates on one-way speech quality in networks. It gives no guidance on how to evaluate systems that include equipment such as echo cancellers or in which interactive impairments such as talker echo are significant. The perceived quality in such cases depends not only on the one-way performance, but very much on the behaviour of the equipment under duplex conditions; specifically, the influence of double-talk and delay needs to be considered. Although all assessments of overall speech quality are ultimately subjective because they depend on the user's opinion, a distinction is made between: subjective methods, which involve real time user assessment; and objective methods, which use stored information on the user's assessment and therefore involve some degree of calibration. Objective methods for the evaluation of speech quality fall into three categories: a) Comparison Methods: Methods based on the comparison of transmitted speech signal and a known reference. b) Absolute Estimation Methods: Methods based on the absolute estimation of the speech quality (i.e. there is no known reference signal); e.g. INMD (ITU-T Recommendation P.561. c) Transmission Rating Models: Methods that derive a value for the expected speech quality from knowledge about the network; e.g. ETSI Model ETR 250, ITU-T Recommendation G.107.