ificance (weight) of the transmitted word. For near instan- required. taneous companding, the scale factor is transmitted less frequency (for example, once every 32 samples), its value being determined by the peak signal level during the complete group of 32 samples. 57.2.10.1 One carrier systems (with FM subcarriers) NICAM-3 encodes the audio samples to 14 bits, placing each block of 32 samples (one millisecond) into one of five ranges, The Japanese FM/FM system (1978) in which the subcarrier is determined by the largest value sample within the block. By dis- locked to the second harmonic of the line frequency (31.5kHz for carding leading zeroes and MSBs according to the range, this 525 line systems) with a switching (AM) subcarrier at 55kHz. Cable distribution systems 57/17 The American BTSC/MTS system (Broadcast Television Systems stream comprising 728 bit frames each of 1 ms duration, giving a bit Committee/Multichannel Television Sound) is derived from the rate of 728kbit/s. The audio signals are sampled at 32kHz with an pilot tone FM stereo system used in radio broadcasting but with a initial resolution of 14 bits/sample and near instantaneous com- pilot frequency (15.734kHz) locked to the video line frequency and pression to 10 bits/sample in 32 sample blocks. Error protection with 'dBx' noise reduction. There is provision for a 15kHz stereo comprises one parity bit added to each 10 bit sample to check the quadrature channel plus a 10kHz monophonic 'second audio chan- six most significant bits. The transmission of the conventional mono nel' (sap) on a low level subcarrier at five times the vision line channel is unaffected. frequency and, where required, an engineer's order wire ('profes- The characteristics of NICAM-728 for television standards G.1 sional channel') on a subcarrier at six times the vision line fre- are shown in Table 57.6. quency. Cable distribution systems 57.2.10.2 Two carrier systems Since the early days of television broadcasting, cable distribution The German dual channel system for s