1、ITU-T RECNN*J*21 74 4862571 0595876 237 INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU J.21 (ex CMTT.505-4) (08/94) TELEVISION AND SOUND TRANSMISSION PERFORMANCE CHARACTERISTICS OF 15 kHz-TYPE SOUND-PROGRAMME CIRCUITS - CIRCUITS FOR HIGH QUALITY MONOPHONI
2、C AND STEREOPHONIC TRANSMISSIONS ITU-T Recommendation 5-21 (Formerly Recommendation ITU-R CMlT) ITU-T RECflN*J-ZL 94 4862591 0595877 173 FOREWORD The -T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The IT-T is responsible for stu
3、dying 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 study by the ITU-T Study
4、 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). ITU-T Recommendation 5.21 was revised by ITU-T Study Group 9 (1993-1996) and
5、 was approved under the WTSC Resolution No. 1 procedure on the 22nd of August 1994. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. L O ITU 1995 All rights reserved. No part of
6、 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 Application . ; 1 . 2 Interface characteristics 1 2.1 Test conditions 1 2.2 Impedance . 1 2.3 Leve
7、ls 2 3 Overall performance 2 3.1 Common parameters . Additional parameters for stereophonic programme transmission . Additional requirements for digital systems . . 2 5 6 3.2 3.3 Annex A - The measurement of non-linearity in the upper frequency range . 7 Recornendation 5.21 (08194) 1 ITU-T RECMN*J-Z
8、L 94 4862591 0595879 TL)b = SUMMARY This Recommendation contains design objectives for equipment to be developed for the transmission of high-quality type sound-programmes. It gives the parameters to be envisaged and appropriate quality values. Measuring methods for several parameters are specified.
9、 11 Recornendation 5.21 (08/94) ITU-T RECMN*J.ZL 94 W 48b259L 0595880 768 Recommendation 5.21) PERFORMANCE CHARACTERISTICS OF 15 kHz-TYPE SOUND-PROGRAMME CIRCUITS - CIRCUITS FOR HIGH QUALITY MONOPHONIC AND STEREOPHOMC TRANSMISSIONS2) (1974; revised 1978, 1982, 1986, 1990 and 1994) The ITU-T, conside
10、ring (a) (b) (cl techniques, particularly for mixed analogue and digital circuits, that it is necessary to set transmission standards for sound-programme circuits; that quality requirements for the hypothetical reference circuit are established for analogue sound programmes; that advantage should be
11、 taken of the technical evolution made possible by the introduction of digital recommends that, with due regard to the application constraints, equipment for new circuits shall meet the requirements laid out below. 1 Application This Recommendation applies to homogeneous analogue or mixed analogue-a
12、nd-digital circuits. The requirements below apply to the hypothetical reference circuit (HRC) defined in Recommendation J.11 (formerly ITU-R Recommendation CMT.502). For estimation of the performance of circuits shorter or longer than the HRC, see ITU-T Recommendation CMTT.605. NOTES 1 2 For all-dig
13、ital circuits, a separate Recommendation might be envisaged after further study. For further information, -R Report CMTT.496 may be consulted. This Report also draws attention to certain differences between CCIR and OIRT Recommendations. 2 Interface characteristics 2.1 Test conditions When circuit p
14、erformance is to be measured, the c system output shall be terminated by a balanced test load, nominally 600 R resistive. 2.2 Impedance System input impedance System output impedance, provisionally 600 R balanced3) Low, balanced Formerly ITU-R Recommendation CMT.505-4. *) For the definition of absol
15、ute power, relative power and noise levels, see ITU-R Recommendation V.574. 3, The tolerance, permitted reactance and degree of unbalance need further study. Recommendation 5.21 (08/94) 1 ITU-T RECMNJJ-21 94 4462591 0595441 bT4 M The open-circuit output level shall not decrease more than 0.3 dB with
16、in the nominal frequency range, if the output is terminated by the specified test load. The reactive part of the source impedance must be restricted to 100 R maximum (provisional value) within the nominal frequency range. This clause alone would however, not rule out a large difference in the reacti
17、ve parts of the output impedances of a stereophonic pair, and this in turn could lead to difficulties in meeting 3.2.2. This aspect needs further study. 2.3 Levels Input maximum programme levei Insertion gain (1 kHz at -12 dBmOs) Adjustment error, within Variation over 24 hours not to exceed Relativ
18、e level (see Recommendation J. 14) +9 dBmOs O dB f 0.5 dB f 0.5 dB +6 dBrs If broadcasting organizations wish to have closer tolerances, it is necessary for the receiving broadcasting organization to insert additional trimming attenuators. 3 Overall performance 3.1 Common parameters 3.1.1 Gainlfrequ
19、ency response See Table 1. Reference frequency: The response shall be measured at: 1 kHz (nominal value) -12 dBmOs If broadcasting organizations wish to have closer tolerances, it is necessary for the receiving broadcasting organization to insert additional equalizers. TABLE UJ.21 I Frequency (kHz)
20、I Response(dB) I 0.04 I f c 0.125 0.125 2 f iG 10 10 e f I 14 I4 fi), are normally of the same order of magnitude and the amplitude levels are usually identical. The particular difference components at frequenciesf2 -fi and 2fi -f2, which fall within the system bandwidth, are used to reflect the sec
21、ond and third order non-linearities, respectively. Table A.l summarizes several methods for the non-linearity measurement. The first method A is the method specified in the main text of this Recommendation. Method B uses two measuring frequencies very close together. Method C uses frequencies furthe
22、r apart. Method D is described in Annex V to -R Recommendation BS.644. The measuring equipment may use either selective filters to improve the protection against noise, or a low-pass filter to measure simultaneous distortions of various orders including other intermodulation components (e.g. intermo
23、dulation with PCM sampling frequencies, or in FDM multiplex). TABLE A. UJ.21 Proposed methods of measurement Method Proposed level of each tonel (Note 1) A I 5 600 1 7 20Q I +3 dBmOs (ITU-T Recommenda-tion J.21) 7 200 6 800 +3 dBmOs 13960 14040 -9dBmOs III B (Note 2) (Note 2) 1600 +3 dBmOs 1600 +3 d
24、BmOs 80 I +9dBmOs 1 13880 I +3dBmOs 1 (No + 18 dB) (No + 12 dB) NOTES 1 B, the levels quoted are for 50 ps pre-emphasis. 2 These levels depend significantly on the pre-emphasis used. In method A, the levels quoted are for no pre-emphasis. In method The level to which the distortion components are referred. 8 Recommendation J.21 (08194)
