In article ,
Jim Lesurf wrote:
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...

There are a number of options in the TV menu for the digital output. Most
of which I don't understand. It is set to PCM and stereo.

If you're interested, I'll wright them all down. The STB seems to have
less options - although I'm using HDMI via the TV for it rather than its
Toslink to the external sound system.

Which is actually more convenient as the mute button still works which is
doesn't on the TV when sending digital. Which seems silly to me.


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.

Thanks Jim. That does sound a logical explanation.

--
*I'm reading a book about anti-gravity. I just can't put it down.*

Dave Plowman London SW
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