1、 ITU-T RECMN*G.LLS 96 4862593 0635223 360 INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMU N KATION STANDARDIZATION SECTOR OF ITU G.115 (02/96) TRANSMISSION SYSTEMS AND MEDIA GENERAL CHARACTERISTICS OF INTERNATIONAL TELEPHONE CONNECTIONS AND INTERNATIONAL TELEPHONE CIRCUITS MEAN ACTIVE SPEECH L
2、EVEL FOR ANNOUNCEMENTS AND SPEECH SYNTHESIS SYSTEMS ITU-T Recommendation G.115 (Previously “CCITT Recommendation“) - ITU-T RECMN*G.335 96 4862571 Ob35224 OT7 = FOREWORD The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The -
3、T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for
4、study by the IT-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). IT-T Recommendation G.115 was prepared by IT-T Study
5、Group 12 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 6th of February 1996. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1996 All righ
6、ts reserved. 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 the ITU. CONTENTS Page 1 Introduction 1 2 Recommended level . 1 3 Measuring method 1 4 Reference poin
7、t 2 References . 2 Recommendation G.115 (02/96) 1 ITU-T RECMN*G*LLS 9b 4Bb259L ObL522b 97T SUMMARY This Recommendation contains a recommendation for the mean active speech level to be used for setting the levels of announcement machines and speech synthesis systems in the telephone network. A level
8、of -19 dBmO is recommended, which presumes that the SLR of the telephones in the network is 8 dB, the long-term target value (referred to a O dBr point). If the present SLR in a national network is different, the recommended level can be adjusted, using a formula supplied, to a level consistent with
9、 that of live speech in the network. The recommended level is defined at the O dBr point, and to measure the level a speech voltmeter conforming to the requirements of Method B speech level meters in Recommendation P.56 should be used. 11 Recommendation G.115 (0196) Recommendation G.115 MEAN ACTIVE
10、SPEECH LEVEL FOR ANNOUNCEMENTS AND SPEECH SYNTHESIS SYSTEMS (Geneva, 1996) 1 Introduction With the deployment of automatic announcement systems and of speech synthesis systems in the telephone network, it is necessary to specify the proper level of the generated speech. The actual speech levels of l
11、ive speech in the network depend on the send and receive efficiencies of the telephone sets. Recommendation P.310 specifies long-term objectives for the SLR and RLR of digital telephone sets. Different networks have different values of SLR and RLR in their telephones. Thus, the speech levels vary fr
12、om one network to another. Information on actual speech levels in different networks and for different types of calls, e.g. national and international, is found in i. A recommendation on speech levels must take these differences into account. In this Recommendation, a recommended level based on the
13、long-term SLR and RLR objectives is provided. As an option, a formula for adjusting the level to that of a particular network is also provided. 2 Recommended level It is recommended that the mean active speech level generated in announcement machines in the telephone network be set to a nominal outp
14、ut level of -19 dBmO. This value presumes that the target value for SLR is 8 dB, referred to a O dBr point. Together with the target value for RLR of 2 dB, the recommended value of -19 dBmO will produce an average listening level at the subscribers end that corresponds to the preferred listening lev
15、el, as defined in Recommendation P. 10. The recommended speech level also conforms with the existing levels in national networks, if the present SLR values are around 8 dB. If the national transmission plan for the present mixed analogue-digital network states a nominal SLR, (referred to a O dBr poi
16、nt) that differs significantly from 8 dB, an interim value for the level from announcement machines and synthesis systems which conforms better with the present levels in the network may be achieved by a correction for the difference. The correction, C = 8 - SLR, dB, is added to the recommended valu
17、e of -19 dBmO, in order to produce a higher or lower level, depending on the sign of the correction. By this correction, the interim level becomes: L, = -19 + C dBmO, which is equivalent to: L, = -1 1 - SLR, dBmO. NOTE - For synthetic speech, it should be checked that the level balance between the i
18、ndividual words in an announcement, in particular for digits, is the same as for real speech. 3 Measuring method The active speech level shall be measured in accordance with P.56 Method B. The necessary precision can be obtained for a duration of speech of at least 5 seconds. For longer announcement
19、s than 20 seconds, it is recommended that at least 20 seconds of active speech be measured. Instead of a speech signal, an artificial voice signal according to Recommendation P.50 may be used for setting the level. Recommendation 6.115 (02496) 1 4 Reference point The reference point for the recommen
20、ded speech level is O dBr as defined in Recommendation G.121. References HI 121 31 ITU-T COM 12-R 9-E (1994). Report of WP 3/12 meeting (Geneva, 23-24 February 1994), page 15, Table 1. ITU-T COM 12-50-E (1999, Basis for Recommendation G.115 on speech levels, (Rapporteur Q.17/12). IT-T Recommendation
21、 P.3 10 (1996), Transmission characteristics for telephone band (300-3400 Hz) digitai telephones. ITU-T Recommendation P.10 (1993), Vocabulary of terms on telephone transmission quality and telephone sets. IT-T Recommendation P.56 (1993), Objective measurement ofactive speech levei. ITU-T Recommendation P.50 (1993), Artificial voices. ITU-T Recommendation (3.121 (1993), Laudness Ratings (Us) of national systems. 141 151 61 71 2 Recommendation G.115 (OZ96) -
