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surround sound and downmix options

i have several related questions, but answers to the first ones may make the remainder pointless:

1. are any of the current freeview HD channels broadcast in 5.1 surround sound or do they only reach the tivo  as plain stereo. NB the Tivo gets them via Virgin's cable  ofr truly " over air" so the real question is not " how are they broadcast" but  " how does Virgin deliver them "

2 if programs arrive as 5.1 are they recorded with that intact.

3. The tivo audio output has options : of  dolby (if present) or downmix to PCM stereo. Mine was set to dolby ( the default ? ). [ the question of where any compression from true 5:1 to  dolby simulated surround takes place in teh delivery chain is not actually relevant to my issue - but it would be interesting to have the lowdown on that also ]

With a standard LED HD TV, I assume any incoming via HDMi surround signal is downmixed to stereo anyway by the TV ( as TVs will only output 2 channel digital audio [because of HDCP rules] and only have 2 inertnal speakers). So does it /should it matter at all whether the downmix is done by the tivo or the TV

4. what prompted all of this: Well, playing back this weekend's the bridge s03 E03 recorded from BBC4 HD, they seems to be some slight echo or distort on some ( not all ) of the dialogue & I dunno if this is a broadcast glitch, a recording glitch, or a downmix issue.  Google tells me that BBC turned OFF surround sound on BBC 4 in 2014 due to glitches but that is an old report, I cannot find it then subsequently turned it back on.

Any advice or insights welcome.

PS we were lsitening to both the TV speakers and to an external amped audio : TV optical out , via a Lindy dac converter into analogue for 2 channel hifi, but we use that setup all the time and other shows are fine.

Also the echo was not constant, which is would be if I had a timing error on my external audio - , it was only a subtle distortion only on some of the speech, maybe linked to where the character was standing/facing which is why I suspect a faulty downmix. It being in Swedish did not help in describing the sound! - but as I said above, I have not noticed any issues on other (English) BBC shows e.g. The last Kingdom, which we have been recording and watching in HD

so the audio chain was Tivo HD recording -> HDMi ->Samsung  TV -> Tv speakers + optical out -> external hifi



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