TABLE OF CONTENTS As stated earlier, the four bits of auxiliary data in each subframe may be used for additional LSBs of audio resolution, if more than 20 bits of audio data are needed per sample. Alternatively the auxiliary data may be used to carry information associated with the audio channel. In many items of equipment manufactured to date they remain unused.
It was proposed to the CCIR in 1987 that the aux bits would prove useful for a good voice quality channel which could be used for coordination (talkback) purposes in broadcasting21. Typically in a radio broadcast studio the programme source (say a studio) sends a stereo programme to a destination (say a continuity suite) along with a good voice quality link for coordination purposes (see Figure 4.8). A feed of cue programme (normally mono), together with a coordination channel and perhaps additional data, is returned from the destination. It was proposed that in digital studio environments all of these signals could be carried over a single standard two-channel interface in each direction by sampling the coordination voice channel at exactly one-third of the main audio's sampling frequency and coding it linearly at 12 bits per sample, resulting in a data rate exactly one-fifth that of the main audio channel. (Main audio channel @ 48kHz, 20 bits; Data rate = 960 000 bits per second; Coordination channel @ 16kHz, 12 bits; Data rate = 192 000 bits per second.) At such a data rate,...
