Function Reference
NICAM Sound
5
5-43
The control information bits CO to C4 have the following functions:
CO Frame Flag Bit.
C1, C2, C3 Application Control Bits (transmission mode).
C4 Reserve Sound Switching Flag (RSSF).
It is set to high (1), if the FM/AM channel transmits the same program
as the NICAM channel; otherwise, it is set to LOW (0).
The frame structure of the NICAM-728 data signal is shown in Figure 5-29.
Figure 5-29. Structure of a 728-bit Frame with a Stereo Sound Signal (before interleaving)
The sound data are split into blocks of 704 bits each and afterwards interleaved according
to the system; a set of 24 control bits is added. A scrambling without Frame Alignment
Word (FAW) serves for equal energy dispersal. This data stream serves for phase shift
keying of the unmodulated carrier (4QPSK modulation).
A spectrum shaping (cosine roll-off) of 100% is used for the sound data in the NICAM I
system; all other NICAM systems have 40% cosine roll-off.
The RF frequency spectrum for NICAM B/G and NICAM I is shown in the Appendix D
.
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