1、 International Telecommunication Union ITU-T P.505TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (11/2005) SERIES P: TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS Objective measuring apparatus One-view visualization of speech quality measurement results ITU-T Recommen
2、dation P.505 ITU-T P-SERIES RECOMMENDATIONS TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS Vocabulary and effects of transmission parameters on customer opinion of transmission quality Series P.10 Subscribers lines and sets Series P.30 P.300 Transmission standards Serie
3、s P.40 Objective measuring apparatus Series P.50 P.500 Objective electro-acoustical measurements Series P.60 Measurements related to speech loudness Series P.70 Methods for objective and subjective assessment of quality Series P.80 P.800Audiovisual quality in multimedia services Series P.900 Transmi
4、ssion performance and QoS aspects of IP end-points Series P.1000 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. P.505 (11/2005) i ITU-T Recommendation P.505 One-view visualization of speech quality measurement results Summary Nowadays, the numerous complex paramet
5、ers that determine the speech quality of telecommunication equipment as well as the end-to-end speech quality can be interpreted by technical experts only. This Recommendation provides a novel quality representation methodology which is easy to use and also easy to understand for non-experts and whi
6、ch can serve as a basis for commercial decisions on a management or marketing level. Source ITU-T Recommendation P.505 was approved on 29 November 2005 by ITU-T Study Group 12 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. P.505 (11/2005) FOREWORD The International Telecommu
7、nication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with
8、 a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recom
9、mendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for co
10、nciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommend
11、ation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
12、 INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Righ
13、ts, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementor
14、s are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2006 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. P.505
15、(11/2005) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Introduction 2 4 Derivation of the one-view visualization methodology 2 5 Selection of parameters. 4 6 Scaling of axes 5 Annex A Examples of the application of the OVV methodology 7 A.1 Application of the OVV methodology to cellphones . 7 A.2 A
16、pplication of the OVV methodology to VoIP terminals 11 A.3 Application of the OVV methodology to VoIP gateways 14 A.4 Further considerations for OVV application to end-to-end configurations 17 Appendix I Analysis examples . 18 I.1 Analysis examples of different cellphones. 18 I.2 Analysis examples o
17、f different VoIP terminals 20 I.3 Analysis examples of different VoIP gateways 22 ITU-T Rec. P.505 (11/2005) 1 ITU-T Recommendation P.505 One-view visualization of speech quality measurement results 1 Scope This Recommendation provides a novel quality-representation methodology of parameters that de
18、termine the speech quality of telecommunication equipment as well as the end-to-end speech quality. This methodology is easy to use and also easy to understand for non-experts and it can serve as a basis for commercial decisions on a management or marketing level. This Recommendation does not provid
19、e methods for the acquisition of speech quality measurement results; it is assumed that the user of this Recommendation has readily at hand those test results which are needed as an input for the representation methodology recommended here; furthermore, this Recommendation does not state any require
20、ments with respect to the parameters mentioned herein. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Reco
21、mmendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularl
22、y published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. 1 ITU-T Recommendation P.340 (2000), Transmission characteristics and speech quality parameters of hands-free terminals. 2 ITU-T Recommendation P.501 (2000
23、), Test signals for use in telephonometry. 3 ITU-T Recommendation P.502 (2000), Objective test methods for speech communication systems using complex test signals. 4 ITU-T Recommendation P.800.1 (2003), Mean Opinion Score (MOS) terminology. 5 ITU-T Recommendation P.862 (2001), Perceptual evaluation
24、of speech quality (PESQ): An objective method for end-to-end speech quality assessment of narrow-band telephone networks and speech codecs. 6 ITU-T Recommendation G.168 (2004), Digital network echo cancellers. 7 ITU-T Recommendation G.711 (1988), Pulse code modulation (PCM) of voice frequencies. 8 I
25、TU-T Recommendation G.723.1 (1996), Dual rate speech coder for multimedia communications transmitting at 5.3 and 6.3 kbit/s. 9 ITU-T Recommendation G.729 (1996), Coding of speech at 8 kbit/s using conjugate-structure algebraic-code-excited linear prediction (CS-ACELP). 10 VDA HFT V 1.5: (2004), Test
26、 specification for hands-free terminals. 2 ITU-T Rec. P.505 (11/2005) 3 Introduction Due to the increasingly implemented signal conditioning, the quality of modern telecommunication equipment (cellphones, VoIP terminals and gateways) can only be described by using the most advanced measurement and a
27、nalysis methods. The reason is obvious: signal processing mechanisms, which until recently were found in hands-free terminals only (echo compensation, noise reduction, voice controlled attenuation and amplification adjustments), are now employed in virtually all modern telecommunication devices. The
28、 implementation of these demanding signal-processing mechanisms is necessary because, on the one hand, cellphones and other terminals are used in very noisy environments and, on the other hand, their geometry continues to be minimized. Therefore, the built-in loudspeaker and microphone cannot be aco
29、ustically de-coupled in a sufficient manner. Echo-reducing measures such as those that are typically used in hands-free terminals are required. In addition, the different algorithms implemented influence each other. This principle is independent of manufacturers; however, the implementations themsel
30、ves are not. This leads to significant differences in quality. The quality of modern terminals (and network equipment) is characterized by numerous speech quality parameters. In order to allow a reliable quality statement, and to detect possible quality problems in advance by laboratory measurements
31、, the telecommunication devices brought to market typically undergo intensive speech quality tests. During these measurements all parameters related to the implemented signal processing and relevant to speech quality are measured and the limit value violation is tested. These measurements guarantee
32、the best possible assessment of speech quality problems that may occur during real use of the corresponding telecommunication device. However, since the numerous complex parameters determining the speech quality of modern telecommunication equipment, as well as the end-to-end speech quality, can be
33、interpreted by technical experts only, a quality representation is required which is easy to use and also easy to understand for non-experts and which can serve as a basis for commercial decisions on a management or marketing level. Another desirable aspect of these measurements is to show the most
34、important parameters in a visual representation, thus giving a quick overview of all speech quality parameters. This representation should reveal at one glance the strengths and weaknesses as well as the limit value violations. 4 Derivation of the one-view visualization methodology The requirements
35、for the one-view visualization (OVV) methodology can be summarized as follows: Quick and easy recognition of expected speech quality problems for selected parameters (limit value violation); Assessment of strengths and weaknesses of signal processing implemented in a terminal or other telecommunicat
36、ion equipment, including end-to-end considerations (quality statement); Easy comparison of different equipment or connections based on the corresponding representations; Easy extension of the representation by new parameters relevant to quality in the future. ITU-T Rec. P.505 (11/2005) 3 A represent
37、ation based on circle segments (“pie diagram“, “star plot“) is recommended (see Figure 1). Figure 1/P.505 Representation “Pie diagram“ (Example with fictitious values of a cellphone) The number of the represented parameters determines the size of the individual circle segments. Similar to a “cobweb“
38、 representation the axes are shown with a common origin. The individual circle segments have the same size (spanned angle 360/number of selected quality parameters). It is recommended that the number of different parameters visualized in one diagram should not exceed twelve. Moreover, the representa
39、tion of individual segment sizes is not interdependent, thus guaranteeing the independence of the different quality parameters from each other. Therefore, this pie diagram offers the following advantages: Independent representation of individual quality parameters. Segment sizes are determined by th
40、e number of selected parameters and are identical. In a possible extension step the segment size could be adjusted according to the contribution of individual speech quality parameters to total quality. However, unless such a measure or weighting rule is available, an identical segment size is recom
41、mended. Segment size (radius) is a measure for the quality of a phone regarding this parameter. By means of a suitable axis scaling, a concentric circle around the origin can be defined which represents a minimum quality measure. Falling below this segment size (radius) indicates a non-compliance wi
42、th this limit value. By means of a suitable colour selection results lying within the tolerance or transgressing the limit values can be easily visualized. Figure 1 gives a representation example for a selection of 10 parameters. Note that this representation does not correspond to a real phone, but
43、 only serves as an example. It easily reveals the strengths and weaknesses as well as the limit value violation of a single device and by representing the results of different devices on one sheet, an easy comparison of the different implementations is possible. 4 ITU-T Rec. P.505 (11/2005) 5 Select
44、ion of parameters It is the responsibility of the user of this Recommendation to select a set of parameters as an input for the OVV methodology. Based on recent experience with speech quality tests, this clause provides a list of parameters that may be considered; this list is by no means exhaustive
45、 and does not exclude the use of additional or other parameters. In sending direction (uplink) Send loudness ratings (in dB); MOS-LQO value 41. NOTE 1 The listening speech quality determined by MOS-LQO or by the objective MOS-value can be used to show the system performance under different packet-lo
46、ss conditions, in addition to the listening speech quality with no packet loss. In receiving direction (downlink) Receive loudness rating (in dB); MOS-LQO value 41. (See Note 1.) For End-to-end configurations Overall loudness ratings (in dB); MOS-LQO value 4. NOTE 2 The listening speech quality dete
47、rmined by MOS-LQO can be used to show the system performance under different packet-loss conditions, in addition to the listening speech quality with no packet loss. For networks Junction loudness ratings (in dB); MOS-LQO value 4. (See Note 2.) Echo attenuation TCLw value. Double talk performance Ch
48、aracterization according to ITU-T Rec. P.340 1. “Live Call“ Phone behaviour during a test call via a real network. Quality of background noise transmission With simultaneous speech in receiving direction. The modulation of the background noise (level variation), caused by a receive signal and the ec
49、ho cancellation signal processing thus activated in the sending direction, is used as a quality measure. _ 1For electrical connections based on ITU-T Rec. P.862 5, objective MOS-value for acoustical connections currently under study in ITU, alternative methods may be used. ITU-T Rec. P.505 (11/2005) 5 With simultaneous speech in sending direction. The modulation of the background noise (level variation), caused by a send signal, is used as a quality measure. D value calculation. Th
