1、I NTERNATIONAL TELECOM M U N CATION UN ION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU P.300 (1 1/2001) SERIES P: TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS Subscribers lines and sets Transmission performance of group audio terminals (GATS) IT U -T Recomme
2、nd at i on P. 300 ITU-T P-SERLES RECOMMENDATIONS TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS Vocabulary and effects of transmission parameters on customer opinion of transmission quality Subscribers lines and sets Transmission standards Objective measuring apparatus
3、Objective electro-acoustical measurements Measurements related to speech loudness Methods for objective and subjective assessment of quality Audiovisual quality in multimedia services Series Series Series Series Series Series Series Series P. 10 P.30 P.300 P.40 P.50 P.500 P.60 P.70 P.80 P.800 P.900
4、For further details, please refer to the list of ITU-T Recommendations. ITU-T Recommendation P300 Transmission performance of group audio teminals (GATs) Summary This Recommendation provides the speech transmission requirements for Group Audio Terminals (GATS). The associated test methods for verifj
5、mg the specified performances are contained in Annex A. An in-situ procedure for checking and aligning GAT terminals in the field is provided in Appendix I. Reference is made, as far as possible, to other Recommendations applicable to speech terminals for analogue and digital networks. only terminal
6、 configuraions not already covered by these Recommendations are addressed in detail. Source ITU-T Recommendation P.300 is a revision of ITU-T Rec. P.30 (1998). It was revised by ITU-T Study Group 12 (2001-2004) and approved under the WTSA Resolution 1 procedure on 29 November 2001. ITU-T Rec. P.300
7、(11/2001) i FOREWORD The International Telecommunication Union 0 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 questi
8、ons and issuing Recommendations on them with 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
9、on these topics. The approval of ITU-T Recommendations 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 IS0 and IEC. NOTE In this Recommendation, th
10、e expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed
11、 Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, 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
12、received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. o ITU 2002 All rights re
13、served. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from ITU. ii U-T Rec. P.300 (11/2001) CONTENTS 1 2 3 4 5 5.1 5.2 5.3 5 -4 Scope . Normative references Definiti
14、ons and abbreviations . Group Audio Terminals types . Speech transmission charactenstics Handset mode . Headset mode Hands-free mode (single-user facilities) . Hands-free mode (multiple-users facility) Receiving volume control and sensitivity adjustments . 5.4.2 Sensitivity-frequency responses 5.4.3
15、 Loudness Rating 5.4.4 Echo path loss characteristics 5.4.5 Distortion . 5.4.6 Out-of-band requirements 5.4.1 5.4.7 Noise 5.4.8 Delay Annex A . Objective measurement methods for han - headsets; - hands-free (single-user facilities); - hands-free (multiple-users facility). GATs can be designed to pro
16、vide telephone-band andor wideband audio facilities. 2 ITU-T Rec. P.300 (11/2001) 5 Speech transmission characteristics The GAT terminals shall be able to interwork (end-to-end) with analogue (POTS) and digital (ISDN) narrow-band telephone sets, as well as with ISDN videophones and wideband telephon
17、es. As a consequence, the audio standards applicable to these devices also apply to GAT terminals intended for the same network access, as appropriate and as specified below. 5.1 Handset mode For GATs designed for interconnecting with the analogue network access, the same relevant regional requireme
18、nts applicable to POTS telephone sets are also applicable. For GATs designed for interconnecting with the ISDN network access, the requirements and measurement methods of ITU-T Recs. P.310 i and P.311 2 apply, respectively for telephone-band and wideband operations. 5.2 Headset mode In principle, th
19、e requirements for headset operations shall be based on the requirements for handset operations, with the following allowances: O the suitable positioning of the microphone with respect to the Mouth Reference Point (MRP) an appropriate Artificial Ear shall be used and the measurement results shall b
20、e referred to position shall be stated by the manufacturer; the Ear Reference Point (ERP) position as specified in ITU-T Rec. P.57 3. 5.3 Hands-free mode (single-user facilities) The following Recommendations apply to GATs terminals designed for providing hands-free facilities to multiple users by c
21、ombining more single-user facilities. ITU-T Rec. P.340 5 applies to GATs designed for the analogue network access. The requirements and measurement methods of ITU-T Recs. P.342 6 and P.341 7 respectively apply for GATs intended for connection to the ISDN and implementing telephone-band (ITU-T Rec. G
22、.711) or wide band (ITU-T Rec. G.722) speech coding. 5.4 Hands-free mode (multiple-users facility) Multiple users GAT terminals are typically designed for guaranteeing optimum hands-free audio performance when installed in Yypical“ conference rooms (i.e. in “live“ environments with acoustic reverber
23、ation phenomena and background noise). To this purpose, suitable signal processing techniques are frequently used for eliminating the reverberation effects in the transduced signals and/or suppressing the room noise. Performance under real operating conditions can then only be evaluated in the actua
24、l installation environments, whose characteristics can not be specified in a general way. This Recommendation is not then intended to address all the installation conditions of GAT terminals, but specifies their audio performances under reference echo-free conditions. In case this testing environmen
25、t is not compatible with the technical characteristics of specific terminals, their manufacturers are given the option to state alternative, more suitable, acoustic testing environments for carrying out their characterisation. An in-situ testing procedure for checking the correct audio alignment of
26、installed terminals is provided in Appendix I. Guidelines for the placement of microphones and loudspeakers in conference rooms can be found in Supplement 16 of the P-series Recommendations 81. ITU-T Rec. P.300 (11/2001) 3 5.4.1 Due to the wide range of operating conditions, both the sending and rec
27、eiving sensitivity of multiple-user handsfree terminals are generally adjusted at their installation on the basis of the room characteristics and of the distance between the transducers and the users. These adjustment controls shall not be accessible to normal users. An additional user-accessible re
28、ceiving volume control (referred to in the following as “receiving volume control“) can be provided in order to allow the user to establish the optimum listening conditions on the basis of the actual room noise, the number of participants and of other variable factors. Receiving volume control and s
29、ensitivity adjustments 5.4.1.1 Sending sensitivity adjustment The sending sensitivity adjustment is intended to allow for varying the positioning of the microphone(s) with respect to the user(s), according to the installation environment constraints. The manufacturer shall state the regulation range
30、 of this control and the microphone-to-speaker nominal operating distance (d$ for which the terminal submitted to the tests has been adjusted. 5.4.1.2 Receiving sensitivity adjustment The receiving sensitivity adjustment is intended to allow for varying the positioning of the loudspeaker(s) with res
31、pect to the user(s) according to the installation environment constraints. The manufacturer shall state the regulation range of this control and the loudspeaker-to-listener nominal operating distance (4) for which the terminal submitted to the tests has been regulated. 5.4.1.3 Receiving volume contr
32、ol Unless stated otherwise, the compliance requirements here provided refer to the maximum position (maximum sensitivity) of the receiving volume control (when manually adjustable). The dynamic range of the receiving volume control (when manually adjustable) shall be of at least 15 dB. 5.4.1.4 Adapt
33、ive gain control An adaptive gain control, sensible to the background noise level, may be implemented into the GAT. Its action should result into complementary and symmetical gain variations, in the receiving and in the sending paths, as a function of the ambient noise level. 5.4.2 Sensitivity-frequ
34、ency responses ITU-T Rec. P.340 SI applies to GATs designed for the analogue network access. The requirements of ITU-T Recs. P.342 6 and P.341 7 respectively apply for GATs intended for connection to the ISDN and implementing telephone-band (ITU-T Rec.G.711) or wideband (ITU-T Rec. G.722) speech cod
35、ing. 5.4.3 Loudness Rating ITU-T Rec. P.340 SI applies to GATs designed for the analogue network access. For GATs intended for connection to the ISDN the following applies. 5.4.3.1 Sending The nominal value of Sending Loudness Rating (SLR) shall be: SLR = (+ 13-FS) dB where F, is as defined in A. 1.
36、1.1. 4 ITU-T Rec. P.300 (11/2001) 5.4.3.2 Receiving The nominal value of Receiving Loudness Rating (RLR) shall be: RLR = (+ 2-Fr) dB for GATs implementing telephone-band (ITU-T Rec. G.711) speech coding and RLR = (+ 5-Fr) dB for GATs implementing wide band (ITU-T Rec. G.722) speech coding. In the ab
37、ove formulae F, is as defined in A. 1.1.2. The volume control range should span the value of the receiving loudness rating equal to that of the corresponding handset telephone, as well as an FUR value about 10 dB lower. 5.4.4 Echo path loss characteristics The requirements of ITU-T Recs. P.342 6 and
38、 P.341 7 respectively apply for the telephone band and wideband operations of GATS intended for connection to the ISDN. 5.4.5 Distortion The requirements of ITU-T Recs. P.342 6 and P.341 7 respectively apply for GATs intended for connection to the ISDN and implementing telephone-band (ITU-T Rec. G.7
39、11) or wideband (ITU-T Rec. G.722) speech coding. 5.4.6 Out-of-band requirements The requirements of ITU-T Recs. P.342 6 and P.341 7 respectively apply for GATs intended for connection to the ISDN and implementing telephone-band (ITU-T Rec. G.711) or wideband (ITU-T Rec. G.722) speech coding. 5.4.7
40、Noise 5.4.7.1 Sending The requirements of ITU-T Recs. P.342 6 and P.341 7 respectively apply for GATs intended for connection to the ISDN and implementing telephone-band (ITU-T Rec. G.711) or wideband (ITU-T Rec. G.722) speech coding. 5.4.7.2 Receiving Irrespectively from the speech coding implement
41、ed, the A-weighted noise produced in the receiving direction at the measurement point by GATs intended for connection to the ISDN shall not exceed -49 dBPa(A)+F,. 5.4.8 Delay The requirements of ITU-T Recs. P.342 6 and P.341 7 respectively apply for GATs intended for connection to the ISDN and imple
42、menting telephone-band (ITU-T Rec. G.711) or wideband (ITU-T Rec. G.722) speech coding. IW-T Rec. P.300 (11/2001) 5 ANNEX A Objective measurement methods for hands-free, multiple users GATs A.l Introduction This annex describes methods which may be used to measure the speech transmission performance
43、s of hands-free, multiple users, Group Audio Terminals intended for ISDN connection. Unless stated otherwise, the same test conditions apply as specified in applicable ITU-T Recs. as appropriate (Le. ITU-T Recs. P.342 6 and P.341 7 respectively for GATs implementing telephone-band (ITU-T Rec. G.711)
44、 or wideband (ITU-T Rec. G.722) speech coding). A.l.l Testing arrangements The acoustic reference conditions for measurement purposes are free-field within the Reference Sphere. However, for specific designs, it is up to the manufacturer to specify an alternative (reverberant) testing environment. I
45、n this case, the specified measurement conditions shall be stated in the test report. A.l.l.l Sending Two different testing conditions shall be used, according to the type of microphone(s) equipping the GAT terminal: - - Microphones intended for being placed on the table - microphones placed on the
46、table surface in front of one or more speakers: microphone(s) placed elsewhere in the room. The arrangement specified in Figure A. 1, placing each microphone in turn at point B. The other microphones shall be removed from the acoustic field of the Artificial Mouth. Microphones intended for being pla
47、ced elsewhere in the room - The acoustic pick-up port of the microphone shall be placed at the centre of the Reference Sphere in an anechoic environment and the Artificial Mouth shall be placed with the lip plane tangential to the Sphere. The reference axis of the Mouth shall coincide with the x-axi
48、s of the Sphere, while the microphone shall be oriented as specified by the manufacturer. In case of microphones intended to pick up the sounds coming fiom multiple directions (either omni-directional or steered devices), the extreme incidence angles on the horizontal plane as stated by the manufact
49、urer shall be tested, as well as an intermediate incidence direction. The testing angles actually used for measurements shall be stated in the test report. In order to take into account the difference between the reference test positioning and the actual microphone-speaker operating distance ( 20 Log Pm: Acoustic spectrum at MRP. Method 2 The sending sensitivity SJ is given by the following relationship: S, 20L0g VS - 20L0g P, COX - 24 dB where: 20 Log Vs: Electric spectrum; 20 Log Pm: Acoustic spectrum recorded at MRP; Corr: Correction factor
