In article , Dave Plowman (News)
wrote:
Got an odd problem.
Sound from TV goes to an external setup via Toslink, and the volume
can't be adjusted on the TV - ie a proper line out. TV set speakers
switched off.
You don't say if the 'toslink' sends both stereo and surround as stereo
spdif, or sends the surround as 'bitstream'. I'll assume the former for
what I say below...
Have a BT STB (Humax) fed to the TV by HDMI. The volume on that can be
adjusted by the remote in the normal way.
Set both to an SD channel - say BBC1 - and adjust the level from the STB
so it matches the TV when you switch between them. STB says 85 on the
screen.
Now change them both to the same HD channel, say BBC1 again. STB is now,
I'd guess, 6dB louder than the TV on the same channel - enough to annoy.
To make it match has to be reduced to 75.
is it that the TV gets quieter or the STB gets louder?
And all that before any transmitted differences in level between SD and
HD. ;-)
Both TV and STB are set to stereo - and no strange balance from one
which would indicate it might be two channels from 5.1 or whatever.
Seems to exhibit the same behaviour between HD and SD on all channels.
I wonder if the TV/STB treat the *possibility* of surround on HD
differently. i.e. One mixs down to stereo when this happens by applying a
scaledown that is engaged when it detects surround. The other simply adds
the channels. So in effect is preset to give 'the same level' when the rear
and center are added. i.e. it scales down the L and R as if they were Lf
and Rf.
I don't know the current situation, but 1-2 years ago when I was first
looking into HDTV sound and the processing of surround in broadcasts I had
the impression that various parts of the industry weren't actually all
following the same rules for such matters. And that 'standards' were
evolving in a haphazard and 'do first and announce later' way that made it
almost impossible for them all to keep together.
Slainte,
Jim
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