ITU-T J 14-1988 RELATIVE LEVELS AND IMPEDANCES ON AN INTERNATIONAL SOUND - PROGRAMME CONNECTION《数字电缆电视系统的图像主观质量评价》.pdf

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1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 * TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%6)3)/.G0G0!.$G0G03/5.$G0G042!.3-)33)/.2%,!4)6%G0G0,%6%,3G0G0!.$G0G0)-0%$!.#%3G0G0/.!.G0G0).4%2.!4)/.!,G0G03/5.$G0G13G002/2!-%#/%#4)/.)45G134G0G0RecommendationG0G0* (Extract from the “LUEG0“OOK)NOTES1 ITU-

2、T Recommendation J.14 was published in Fascicle III.6 of the Blue Book. This file is an extract from theBlue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, thecontents of the file are identical to the Blue Book version and copyright condit

3、ions remain unchanged (see below).2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1988, 1993All rights reserved. No part of this publication may be reproduced or utilized in an

4、y form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle III.6 - Rec. J.14 1Recommendation J.14Fascicle III.6 - Rec. J.14RELATIVE LEVELS AND IMPEDANCES ON AN INTERNATIONALSOUND-PROGRAMME CONNECTION(former Recommendatio

5、n J.13; amended at Geneva, 1972, 1976 and 1980, and at Melbourne, 1988)1 Level adjustment on an international sound-programme connectionThe CCITT recommends the use of the constant voltage method. If, to a zero relative level point of theinternational sound-programme connection, a zero absolute volt

6、age level is applied (sine-wave signal of 0.775 voltsr.m.s.) at the reference frequency 0.8 or 1 kHz, the absolute voltage level at the output of each sound-programmecircuit (Points B, C, D . . . F of Figure 3/J.13) should be + 6 dB (i.e. 1.55 volts r.m.s.). Therefore these points have tobe regarded

7、 as relative level points of + 6 dBrs according to Recommendations J.21, J.22 and J.23.The zero relative level point is, in principle, the origin of the international sound-programme connection (PointA in Figure 3/J.13). Different conventions may be agreed between the telephone Administration and th

8、e broadcastorganization within a country, provided that the levels on the international sound-programme link are unchanged.A zero relative level point is, in principle, a point at which the sound-programme signals correspond exactlywith those at the origin of the international sound-programme connec

9、tion. At a point of zero relative levels, signalshave been controlled in level by the broadcasting organization such that the peak levels very rarely exceed +9 dBrelative to the peak values reached by a sine-wave signal of 0.775 volts r.m.s. (for a 600-ohm resistor load, when levelsare expressed in

10、terms of dBm).In Recommendation 645, CCIR has defined test signals to be used on international sound-programmeconnections based on existing CCITT Recommendations.2 Diagram of signal levels on an international sound-programme connectionAll signal levels are expressed in terms of r.m.s. values of sine

11、-wave signals with reference to 0.775 volts.The voltage level diagram for an international sound-programme connection, however made up, should be suchthat the voltage levels shown will not exceed the maximum undistorted power which an amplifier can deliver to asound-programme link when a peak voltag

12、e (i.e. +9 dB) is applied to a zero relative level point on the internationalsound-programme connection.With these conditions, +6 dB is the nominal voltage level at the output of the terminal amplifiers of the sound-programme circuits making up the international sound-programme link (Points B, C, D

13、. . . F of Figure 3/J.13).Considering that rare excursions of the permitted maximum signal level may occur, and that adjustment errorsand maintenance tolerance have to be taken into account, sound-programme circuits need a definite overload margin.The amount of this margin is still under study.If a

14、sound-programme circuit which is part of the international sound-programme link is set up on a group in acarrier system, the objective for a new design of equipment is that the relative level of the sound-programme circuit,with respect to the relative level of the telephone channel, should be chosen

15、 such that the mean value and the peakvalue of the load presented by the sound-programme channel should be no higher than that of the telephone channelswhich are replaced by the sound-programme channel. The effects of pre-emphasis and compandors should, wherepresent, be taken into consideration.It i

16、s recognized that this condition may not be observed in all cases, particularly in certain existing types ofequipments. It is recommended that in those cases the zero relative level points of the sound-programme circuit and ofthe telephone channels should coincide.It might be as well, however, if th

17、e equipment could, where possible, tolerate a maximum difference of 3 dBbetween the relative levels of the sound-programme and telephone transmissions, so that the best adjustment can beobtained, depending on any noise or intermodulation present, but at the same time observing the constraints impose

18、dby the considerations on loading.2 Fascicle III.6 - Rec. J.14Note The relative level at which the modulated sound-programme signal is applied to the group link is givenin Recommendations J.31 for 15 kHz-type circuits, J.34 for 7 kHz-type circuits and in the Annex to RecommendationJ.22 for 10 kHz-ty

19、pe circuits.3 Definitions and abbreviations for new sound-programme signalsDefinitions and symbols are in current use to define relative levels for telephony. However, additionaldefinitions and symbols are necessary for the absolute and relative levels in respect of sound-programme signals. Thecorre

20、sponding definitions and symbols for telephony and sound-programme signals are given below.3.1 dBm01)The absolute signal power level, in decibels, referred to a point of zero relative level.3.2 dBr1)The relative power level, in decibels.3.3 dBm0sThe absolute signal power level, in decibels, referred

21、 to a point of zero relative sound-programme level.3.4 dBrsThe relative (power) level, in decibels, with respect to sound- programme signals. (This abbreviation is onlyapplicable at points in a sound-programme circuit where the signals can nominally be related to the input by a simplescaling factor.)Note The use of level definitions is given in CCIR Recommendation 574._1)These symbols traditionally relate to telephony relative levels.