Is all the info necessary to define the exact format of the data encoding
always transmitted in an audio digital data stream or is it sometimes
ambiguous ?
Specifically with ITV Digital (assuming it is still around by the time you
read this), do they ever transmit anything apart from standard stereo or
Dolby
Surround ? (I heard not as they don't have the bandwidth). When
they
do transmit Dolby Surround is there anything in the data stream so that you
know it is in surround rather than ordinary stereo ? I do have a digital
output from my Nokia ex OD box.
AFAIK Dolby
Surround
is matrixed onto the stereo channels by phase shifting. This would
mean
that ANY stereo signal (analogue, AC3, PCM) could carry this extra
information (centre and rear mono). The processor (there's that
word again) will do the necessary maths to be able to create these two
pseudo-channels. This is why the frequency response of Dolby Surround
is
so poor compared to Dolby Digital (AC3) which it a digital bitstream
containing data for a number of DISCRETE audio
channels.
Digital output on
you
OD box merely outputs a stereo PCM signal so that you can feed it to an AV
amp
(or other DAC) for converting to analogue and amplification. As
stated
above, the stereo channels COULD contain matrixed audio, but AFAIK PCM
doesn't
carry any flags to show that anything other than bog-standard stereo (or
perhaps mono) is being transmitted.
HTH, James
H