1、CCIR VOLUMES X/XI-2 90 4855212 050b752 5 Rec. 651 RECOMMENDATION 651 DIGITAL PCM CODING FOR THE EMISSION OF HIGH-QUALITY SOUND SIGNALS IN SATELLITE BROADCASTING (15 kHz NOMINAL BANDWIDTH) (Question 2/10 and 11, Study Programme 2F/10 and li) (1986) The CCIR, CONSIDERING (a) that the compromise betwee
2、n quality objectives and bit rate may be different for sound services which may have various quality requirements and planning constraints; they may also vary according to the requirements of individual administrations; (b) that there are clear advantages for broadcasters, receiver manufacturers and
3、 the public in using a single standard for each application; - UNANIMOUSLY RECOMMENDS 1. emission of audio digital signals in satellite broadcasting having a 15 kHz nominal bandwidth; that where PCM coding is employed (see Note i), the sampling frequency should be 32 kHz for the 2. that when a reduc
4、tion in bit rate is necessary (see Note 2), a non-linear coding law should be used with near-instantaneous companding to reduce the number of bits/sample from 14 to 10. The companding law should have five scale ranges. The selected range is associated with a block of 32 consecutive samples. The pre-
5、emphasis should conform either to CCIT Recommendation 5.17 with an insertion loss of 6.5 dB at 0.8 kHz or to a 50/15 p pre-emphasis, both shown in Fig. 1 (see Note 3); 3. that when the above bit-rate reduction is not necessary (see Note 2), linear coding should be used with 14 bitdsample, with pre-e
6、mphasis as in 0 2 abqve, or, if judged to be needed, a 16-14 bitdsample floating-point system (see Note 4); 4. Note I - Report 953 describes an alternative system of digital coding suitable for high quality sound signals for satellite sound broadcasting employing adaptive delta modulation. Note 2 -T
7、he area of application for this case is related to national requirements. Note 3 - In Region 1, the use of the pre-emphasis given in CCIiT Recommendation 5.17 is preferred. Note 4 - For the case of sound-only broadcasting, studies are still in progress on the subject of emphasis for linear coding. N
8、ote 5 - In both of the above cases (0 2 and 3 above), the number of bitdsample does not include ancillary bits: for example, error-protection bits, or seale factor bits. that in both cases (0 2 and 3 above), 2s complement coding should be used (see Note 5). CCIR VOLUMES X/XI-2 90 4855212 050b753 7 =
9、 10 10 8 6 4 2 .n go 2 2 II -4 k -6 8 -2 -a -10 -12 -14 Rec. 651 5 IO2 2 5 lo3 . 2 5 104 2 Frequency (Hz) FIGURE 1 - Pre-emphasis characteristics Note - Curves correspond to thefollowing formulae: - For Sol15 PS ; Y = 10 log dB I+ (0.05 I+ (0.015 w) - 1 + (9 - - For CCIl!T RecommendationJ.17 ; Y = 10 10s w- 277 - where : - : frequency (kHz) * Attenuation of the pre-emphasis at 800 Hz is set to 6.5 dB.
