1、- _ STDeITU-T RECMN J.54-ENGL L78b 48b257L Ob30090 253 INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU J.54 (ex CMTT.660) 05/86 1 TELEVISION AND SOUND TRANSMISSION TRANSMISSION OF ANALOGUE HIGH-QUALITY SOUND-PROGRAMME SIGNALS ON MIXED ANALOGUE-AND- DIGITAL
2、 CIRCUITS USING 384 kbit/s CHANNELS ITU-T Recommendation J.54 (Formerly Recommendation ITU-R CMlT.660) FOREWORD The IT Telecommunication Standardization Sector (IT-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and t
3、ariff 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, prod
4、uce Recommendations on these topics. ITU-T Recommendation J.54 (formerly Recommendation ITU-R CMTT.660) 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 exis
5、t as of 28 February 1993. In its place, the IT Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRI3 have been replaced by the Radiocommunication Sector (ITU-R). Conforming to a joint decision by the World Telecommu
6、nication 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 telec
7、ommunication 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 mecha
8、nical, including photocopying and microfilm, without permission in writing from the ITU. Recommendation 5.54) TRANSMISSION OF ANALOGUE HIGH-QUALITY SOUND-PROGRAMME SIGNALS ON MIXTED ANALOGUE-AND-DIGITAL CIRCUITS USING 384 kbit/s CHANNELS (1 986) The CCIR, CONSIDERING (a) that high-quality sound-prog
9、ramme signals on mixed analogue-and-digital circuits must satisfy the performance requirements of Recommendation 505; (b/ that the number of analogue-to-digital and digital-to-analogue conversions as well as the number of digital coding techniques should be kept to a minimum, in order for the intern
10、ational sound programme connection to provide the same or higher degree of performance than possible with a homogeneous analogue connection; (9 that the CCITT has recommended a 384 kbit/s HO bearer channel in Recommendation 1.412 which has the capacity to transport sound-programme signals on an inte
11、grated services digital network (ISDN); (4 different primary rates should not introduce any signal degradation, that digital-to-digital conversions using the same encoding law on tandem sound-programme circuits with UNANIMOUSLY RECOMMENDS that the transmission of sound-programme signals on 384 kbit/
12、s channels, with an analogue interface at the input and output of the international connection, should satisfy the analogue-and-digital requirements defined in f 1 and 2 respectively of this Recommendation. Note 1 - Equipment characteristics for the coding of analogue high-quality sound-programme si
13、gnals using 384 kbits channels have been defined in CCITT Recommendation 5.41. Characteristics for equipment offering digital access at 384 kbits into 2048 kbits are given in CCITT Recommendations G.735 and G.737. Note 2 - Other coding techniques are proposed and are the subject of Question 18/CMTT,
14、 for example, coding of analogue sound-programme signals at 3 16 kbit/s, insertion into a 320 kbits channel and multiplexing of six high-quality sound-programme channels within 2048 kbits. Techniques which may be used by bilateral agreement of the administrations concerned are listed in Table I of R
15、eport 647. 1. Analogue requirements performance requirements of Recommendation 505. 1.1 Single codec perjormance The analogue-to-analogue transmission performance of a single codec shall be equivalent to one-third the performance characteristics of the hypothetical reference circuit (see Recommendat
16、ion 505). Where applicable, the lawsof addition given in Recommendation 605 can be used to calculate the single codec performance with n = 3 analogue-to-analogue sections. Transmission of high-quality sound-programme signals on mixed analogue-and-digital circuits shall satisfi the Formerly Recommend
17、ation ITU-R CMTT.660. Recommendation 5.54 (05/86) 1 1.2 Tandem codec performance The hypothetical reference circuit (HRC) given in Recommendation 502 is divided into three sections of equal length which could be either analogue or digital. Each digital section should only contain one encoder and one
18、 decoder. Therefore, in a mixed analogue-and-digital HRC, Table I indicates the number of codecs which may be connected in tandem. O 1 2 3 TABLE I -Number of tandem codecs on a mixed analogue-and-digital sound programme circuit 3 2 1 O Analogue sections Tandem codecs Normalized analogue Normalized a
19、nalogue input (I) output (1) 8160 to 8192 8176 4096 to 4128 41 12 4080 to 4096 4088 2048 to 2064 2056 2040 to 2048 2044 1024 to 1032 1028 1020 to 1024 1022 512 to 516 514 510 to 512 51 1 256 to 258 257 255 to 256 255.5 128 to 129 128.5 127 to 128 127.5 o to 1 0.5 Effective resolution (bits) Compress
20、ed Segment digital code No. 1 9 895 768 2 10 767 640 3 11 639 512 4 12 511 384 5 13 383 256 255 128 127 O 6 14 2. Digital requirements Digital-to-digital conversions using the same encoding law as given in Table II or Table III of this Recommendation on tandem sound-programme circuits with different
21、 primary rates should not introduce any signal degradation. Digital-to-digital conversions using different encoding laws, as given in Tables II and III, should cause minimum signal degradation. TABLE II - Coding tuble for instunfuneous companding of sound-programme signals * * The positive half of t
22、he coding table only is shown. (l) The top code word of k 8192 corresponds to an overload level of +i5 dBmOs at the O dB insertion loss frequency (2.1 kHz) ofthe CCITT Recommendation J.17 pre-emphasis circuit with 6.5 dE loss at 800 Hz. 2 Recommendation 5.54 (05/86) - Range 4 3 2 1 O TABLE III - Cod
23、ing table for near-instantaneous companding of sound-programme signals Normalized analogue input (I) +8176 to +XI92 O to +I6 -16 to0 -8192 to -8176 +4088 to +4096 O to +8 -4096 to -4088 +2044 to +2048 O to+4 -4 too -2048 to -2044 +I022 to +lo24 o to+2 -2 to o -1 024 to -1022 +511 to +512 o to+1 -1 t
24、o o -512 to -511 Normalized analogue output (1) +8 184 +8 -8 -8 184 +4092 +4 -4 -4092 +2046 +2 -2 -2046 +lo23 +I -1 -1023 +511.5 +OS -0.5 -511.5 Compressed digital code +511 O -1 -512 +511 O -1 -512 +511 O -1 -512 +511 O -1 -5 12 +511 O -1 -512 (I) The top code word of f8192 corresponds to an overlo
25、ad level of +I2 dBmOs at the O dB insertion loss frequency (2.1 kHz of the CCITT Recommendation J. 17 pre-emphasis circuit with 6.5 dB loss at 800 Hz. 2.1 Sampling frequency The sampling frequency shall be 32 kHz. The associated tolerance shall be f5 x as specified in CCITT Recommendations G.732 and
26、 G.733 for primary PCM multiplex equipment. This sampling frequency conforms with that given in Recommendation 606. 2.2 Encoding method The recommended encoding laws are based on a uniformly quantized 14-bit per sample PCM technique with companding and shall employ either method (a) or method (b) wi
27、th the appropriate rules of precedence as defined below: (a) eleven-segment 14-to- 1 1 bit instantaneous A-law companding. The companding characteristic is illustrated in Fig. 1; (b) five-range 14-to- 1 O bit near-instantaneous companding. The companding characteristic is illustrated in Fig. 2. Digi
28、tal paths between administrations which have adopted different systems should carry signals encoded according to method (a). Where both administrations have adopted the same method, that method should be used on digital paths between them. Any necessary transcoding will be done by administrations us
29、ing method (b). Recommendation 5.54 (0986) 3 iii 6 Normalized input magnitude dol-cc FIGURE 1 - Instantaneous companding characteristics m M 2 - 1116 llU 114 11Z Normalized input magnitude FIG URE 2 - Near-instantaneous companding characteristics d02sc 2.3 Coding table near-instantaneous compandor i
30、s specified in Table III. 2.4 Bit error protection The coding table for the instantaneous A-law compandor is specified in Table II and the coding table for the 2.4.1 Error detection Error detection shall be used to detect erroneous sound programme samples which can be caused by random bit errors, bu
31、rst errors, frame loss or frame slips. 2.4.2 Error concealment and correction Error concealment or correction techniques shall be used to ensure that the subjective quality of the sound-programme signal is not degraded below grade 4.5 as defined in Recommendation 562. This quality shall be maintaine
32、d for a random bit error ratio of 10 -6 as defined in CCITT Recommendation G.821. Further study is necessary to define a requirement for burst errors (see Report 648). 4 Recommendation 5.54 (05/86) 2.4.3 Frame losshecovery Frame lossrecovery on digital channels causes interruptions to sound-programm
33、e signals. The tolerable limits for these interruptions require further study (see Reports 642 and 647). 2.5 Jitter Jitter characteristics from the digital interface can produce impairments to the decoded analogue signal after passing through a digital system. This requires further study as outlined
34、 in Report 648. 2.6 Transmission bit rate 2.6.1 Monophonic transmission The transmission bit rate for one sound-programme channel shall be 384 kbiis, including all ancillary bits as necessary. 2.6.2 Stereophonic transmission Two separate 384 kbiis channels shall be used to form a stereophonic (stere
35、o-pair) sound- programme circuit. Both sound-programme channels shall be routed together over the same transmission path to avoid transmission delay differences. 2.7 Network access Sound-programme signals coded into 384 kbiis digital channels should interface to the ISDN at 1544 kbits or 2048 kbit/s as specified in CCITT Recommendation 1.412. Recommendation 5.54 (0586) 5 -
