ITU-T G 111-1993 Loudness Ratings (LRs) in an International Connection ((Study Group XII) 21 pp)《国际连接的响度评定值(LRs)传输系统和媒介 整个国际电话连接传输质量的一般建议(研究12组)2》.pdf
《ITU-T G 111-1993 Loudness Ratings (LRs) in an International Connection ((Study Group XII) 21 pp)《国际连接的响度评定值(LRs)传输系统和媒介 整个国际电话连接传输质量的一般建议(研究12组)2》.pdf》由会员分享,可在线阅读,更多相关《ITU-T G 111-1993 Loudness Ratings (LRs) in an International Connection ((Study Group XII) 21 pp)《国际连接的响度评定值(LRs)传输系统和媒介 整个国际电话连接传输质量的一般建议(研究12组)2》.pdf(21页珍藏版)》请在麦多课文档分享上搜索。
1、- ITU-T *RECMN*G-111 93 m 4862591 0587459 295 m INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU G.lll (03193) TRANSMISSION SYSTEMS AND MEDIA GENERAL RECOMMENDATIONS ON THE TRANSMISSION QUALITY FOR AN ENTIRE INTERNATIONAL TELEPHONE CONNECTION LOUDNESS RATIN
2、GS (LRs) IN AN INTERNATIONAL CONNECTION ITU-T Recommendation G.lll (Previously “CCITT Recommendation“) ITU-T *RECflN*G.LLL 93 m 4862591 05894b0 TO7 m FOREWORD The IT Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The IT-T is resp
3、onsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by th
4、e IT-T Study Groups which, in their turn, produce Recommendations on these topics. ITU-T Recommendation G.lll was revised by the IT-T Study Group XII (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecommu
5、nication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to
6、 delay publication of this Recommendation, no change has been made in the text to references containing the acronyms “CCIT, CCIR or IFRB or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the
7、new ITLJ structure. 2 telecommunication administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1994 All rights reserved. No pari of this publication may be reproduced or utilized in any form or by any
8、 means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the . CONTENTS Nominal LRs of the national systems . 1 . 1 Definition of nominal LRs of the national systems 1.2 Recommended values . Nominal overall loss of the international chain LRs and dir
9、ectional effects in a complete connection 3.1 Nominal LRs for each transmission direction 3.2 Traffic-weighted mean values of OLRs 3.3 Difference in transmission loss between the two directions of transmission Variation in time and effect of circuit noise . 4.1 Variations in time . 4.2 Effect of cir
10、cuit noise Practical limits of the OLR between two operators or one operator and one subscriber . Incorporation of PCM digital processes in international connections 6.1 Connections with a digital 4-wire chain extending to the local exchanges 6.2 Mixed analogue/digital connections . Annex A . Explan
11、ations related to Recommendations G . 1 1 I. G.12 1. G . 122. G . 13 1. G . 134: properties and uses of loudness ratings General explanations of loudness rating terms as used in the G-Series Recommendations . Psycho-acoustic model for loudness ratings . Measurement of loudness ratings of telephone s
12、ets Annex B - Recommended values and limits of the loudness ratings for circuits in international connections Annex C - Translation of LR values into CRE values References . A . 1 A.2 A.3 A.4 Application of loudness ratings in the Series-G Recommendations . Recommendation G.lll (03/93) Page 1 1 1 1
13、2 2 2 2 3 3 3 3 4 4 5 5 5 6 7 8 15 16 17 i ITU-T +RECMN+GmLLL 73 48b259L 0589462 88T PREAMBLE Clauses i to 5 of this Recommendation apply in general to all-analogue, mixed analoguedigital and all-digital international telephone connections. However, where Recommendations are made on specific aspects
14、 in clause 6 for mixed analoguddigital or all-digital connections, clause 6 will govern. In the international transmission plan, the loudness rating (LR) between two subscribers is not strictly limited; its maximum value results from various Recommendations. The values given below, either in terms o
15、f LR should be used to verify that international telephone connections provide an adequate loudness of received speech. Administrations employing CREs should preferably translate the LRs of this Recommendation into their national CREs by the methods given in Annex C or, as a second choice, apply the
16、 values given in Volume III of the Red Book (IT, Geneva, 1985). NOTES 1 2 The main terms used in this Recommendation are defined and/or explained in Annex A. For many telephone sets using carbon microphones, the SLR and STMR values can only be determined with limited accuracy. Recommendation G.lll (
17、03D3) ITU-T *RECMN*G.333 93 D 4862593 0589463 71b = Recommendation G.111 LOUDNESS RATINGS (LRs) IN AN INTERNATIONAL CONNECTION (Geneva, 1964; amended at Mar del Plata, 1968; Geneva, 1972.1976 and 1980; Malaga-Torremolinos, 1984; Melbourne, 1988, and Helsinki, 1993) 1 Nominal LRs of the national syst
18、ems 1.1 Definition of nominal LRs of the national systems Send and receive loudness ratings, SLRs and RLRs respectively, may in principle be determined at any interface in the telephone network. In this Recommendation and in Recommendation G.121, the SLRs and RLRs of the national systems are referre
19、d to the Virtual International Connecting Points (VICPs) as defined in 2.12/G.101; see Figure 1. The virtual international connecting point is a point in the international circuit at the International Switching Centre (ISC). The relative levels at the VICP are: - Sending: OdBr; - Receiving: O dBr fo
20、r digital circuits; -0.5 dBr for analogue or mixed analogue/digital circuits. The nominal circuit loss of international circuits at the reference frequency (1020 Hz) is therefore O dB for digital circuits and 0.5 dB for analogue and mixed analoguddigital circuits. NOTES i in digital international ci
21、rcuits, the VICP will be at the digital bit stream. In analogue exchanges, the VICP often will be a hypothetical, not accessible point; see 2.12/G.i01 and 2.13/G.101. 2 Earlier, the Virtual Analogue Switching Points (VASPs) having the relative levels -3SdBr and -4 dBr were used as the reference poin
22、ts. 1.2 Recommended values Recommendation G.121 gives objectives for the nominal SLR and RLR of national systems. 2 Nominal overall loss of the international chain Each international analogue and mixed analogue/digital circuit should in principle have a 0.5 dB loss at 1020 Hz. However, some circuits
23、 can be operated with higher losses (see 2.UG.131) and certain analogue and mixed analoguddigital circuits may be operated at zero loss (see 4.2/G.101). Digital circuits have O dB transmission loss (see clause 6 below). As far as transmission is concerned. there is no strict limit on the number of i
24、nternational circuits which may be interconnected in tandem, provided each analogue and mixed analoguddigital circuit has 0.5 dB nominal loss, and provided there is a 4-wire interconnection. Naturally, the fewer the number of interconnected circuits the better the transmission performance is likely
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