1、INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU J.25 (ex CMTT.605) (05/86) TELEVISION AND SOUND TRANSMISSION ESTIMATION OF TRANSMISSION CIRCUITS SHORTER OR LONGER THAN THE HYPOTHETICAL REFERENCE CIRCUIT PERFORMANCE OF SOUND-PROGRAMME ITU-T Recommendation J
2、.25 (Formerly Recommendation ITU-R CMTT.605) STD-ITU-T RECMN J-25-ENGL L98b m 48b2591 Ob317bU 8T M FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tar
3、iff 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 the ITU-T Study Groups which, in their turn, produc
4、e Recommendations on these topics. ITU-T Recommendation J.25 (formerly Recommendation ITU-R CMTT.605) was elaborated by the former ITU-R Study Group CMTT. See Note 1 below. NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist
5、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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector (ITU-R). Conforming to a joint decision by the World Telecommuni
6、cation Standardization Conference (Helsinki, March 1993) and the Radiocommunication Assembly (Geneva, November 1993), the ITU-R Study Group CMTT was transferred to ITU-T as Study Group 9, except for the satellite news gathering (SNG) study area which was transferred to ITU-R Study Group 4. 2 telecom
7、munication administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1990 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechani
8、cal, including photocopying and microfilm, without permission in writing from the ITU. Recommendation J.25I) ESTIMATION OF TRANSMISSION PERFORMANCE OF SOUND-PROGRAMME CIRCUITS SHORTER OR LONGER THAN THE HYPOTHETICAL REFERENCE CIRCUIT (1 982; revised 1986) The CCIR UNANIMOUSLY RECOMMENDS that for the
9、 estimation of transmission performance of sound-programme circuits shorter or longer than the hypothetical reference circuit the following rules be applied: Laws of addition 1. Comments on the use of the laws of addition The definition of a circuit in terms of a single multiple of the hypothetical
10、reference circuit is impossible if the number of audio-to-audio sections and the length of the circuit differ from those of the hypothetical reference circuit by different ratios, i.e. if n/3 f LI1 where n : number of audio-to-audio sections, L : length of the circuit, I: 2500km. In such cases two d
11、efinitions of the circuit in terms of the hypothetical reference circuit should be used, one for those parameters primarily a function of the circuit configuration, and a second for those parameters (e.g continuous random noise) primarily a function of the length of the circuit. 2. Law pertaining to
12、 circuit configuration For the first definition of the circuit in terms of the hypothetical reference circuit use the following equation for all parameters in Table II except for “continuous random noise”. Let O3 : design objective or the parameter derived therefrom and indicated in Table II, permit
13、ted value for three and O, : performance, or the parameter mentioned above, to be estimated for n sections. homogeneous sections of the hypothetical reference circuit, The following expressions apply: - for absolute values and logarithmic deviations: - for absolute levels: - for logarithmic ratios:
14、*) Formerly Recommendation ITU-R CMIT.605. Error! Error! Recommendation 5.25 (05/86) 1 STD*ITU-T RECMN J-25-ENGL 17Ab 48b2571 Ob31762 b52 Formula (1) h has the value 1, 312 or 2 in accordance with Table II: h = 1 gives linear or arithmetic law of addition, h = 3/2 gives the “three-halves power” law
15、of addition and h = 2 gives the quadratic (rems.) law of addition. Formulas (2) and (3) Calculated values of Error! and Error! are given in Table I. h=2 0.58 0.82 1 .o0 1.15 1.29 1.41 1.53 1.63 I .73 1.83 1.91 2.00 2.08 2.16 2.24 3. Law pertaining to circuit length h=l -9.5 dB -3.5 0.0 2.5 4.4 6.0 7
16、.4 8.5 9.5 10.5 11.3 12.0 12.7 13.4 14.0 For the second definition of the circuit in terms of the hypothetical reference circuit use the following equation for “continuous random noise levels” only. When distance is considered the law of addition becomes: Error! (4) where D, D3, L and I are as defin
17、ed in 5 1 and 5 2. If I 280 km, set I = 280 km in (4). Note - The values calculated as per this Recommendation provide only indications of the probable performance. They should be used with caution when studying the design of equipment, because the laws of addition are not precisely known for every
18、type of impairment. Further studies are necessary, especially to cover the case of mixed analogue-and-digital circuits. TABLE I Error! Error! l- n I 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0.33 0.67 1 .o0 1.33 1.67 2.00 2.33 2.67 3.00 3.33 3.67 4.00 4.33 4.67 5.00 h = 312 0.48 0.76 1 .o0 1.21 I .41 1.59 1
19、.76 1.92 2.08 2.23 2.38 2.52 2.66 2.79 2.92 h = 312 -6.4 dB -2.3 0.0 1.7 3.0 4.0 4.9 5.7 6.4 7.0 7.5 8.0 8.5 8.9 9.3 h=2 -4.8 dB -1.8 0.0 1.2 2.2 3.0 3.7 4.3 4.8 5.2 5.6 6.0 6.4 6.7 7.0 2 Recommendation 5.25 (05/86) - TABLE II Parameter Insertion gain (1 .O kHz) Parameters relevant to mono and stere
20、o circuits Adjustment error Variation during 24 h Gainlfrequency response Group delaylfrequency response referred to minimum Maximum weighted noise level Single tone interference level Ratio of disturbing modulation by power supply to reference signal Non-linear distortion Error in reconstituted fre
21、quency Intelligible crosstalk ratio Error in amplitudelamplitude response Difference in gain between A and B channels Phase difference between A and B channels Intelligible crosstalk ratio between A and B channels Non-linear crosstalk ratio between A and B channels Additional parameters relevant to
22、stereo circuits h Applicable (tentative expressed formula D3 in value) dB 1 2 dB 1 2 dB 1 3 12 ms 1 1 dBqOps 4 2 dBmO 2 312 dB 3 312 YO 1 312 Hz 1 3 12 dB 3 3 12 dB 1 3 I2 dB 1 (9 degree 1 (9 dB 3 312 dB 3 312 (I) Some administrations have found h = 312 appropriate. Tests conducted in Japan CCIR, 1978-821, however, showed bette agreement with quadratic law of addition (h = 2) than 312 law of addition. REFERENCES CCIR Documents 1978-821: CMTTl233 (Japan). Recommendation 5.25 (05/86) 3
