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Multichannel Sound

#1
Does anyone know what the multichanel sound format is? I've just got a LG OLED557b TV and I'm having tremendous problems trying to get sync of A/V with video ahead of sound. This disappears when HDR Fox T2 is in stereo output.
 

Black Hole

May contain traces of nut
#2
Well, seeing as the HDR-FOX carries the Dolby Digital Plus logo...

Stereo is carried on the HDMI as PCM, regardless of input format. Multichannel audio cannot be transported by HDMI without compression - but I confess I don't know whether the audio channel is simply sent to the receiver in the same format it was broadcast (which would be the obvious way to do it) or if some kind of transcoding is going on (in hardware).
 
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rollsjohn

New Member
#3
Thanks for the info BH. I've exhausted settings at both ends of the system but still the problem exists. Seems I'll have to put up with stereeo and PCM since it looks like an insoluble problem. Lots of complaints about lip sync with this TV on other forums but wanted to rule out the Humax being part of it. Looks like manufacturers develop super sound systems using Dolby but when it comes to connecting kit together they don't speak the same language.
 

Black Hole

May contain traces of nut
#4
Does the lip sync setting on the Humax adjust multichannel audio as well, or only when set to stereo?

Lip sync errors are worst when the sound is ahead of the video (which never occurs in real life, so the brain is getting conflicting data). If the video processing chain takes longer to produce the output than the audio processing chain, that's when there are problems. Start with all audio sync adjustments to maximum delay, and if the sound is still ahead of the vision it's stuffed.
 
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rollsjohn

New Member
#5
It's the other way around, BH. The video is ahead of sound. If you watch a news broadcaster the lips start moving before the corresponding sound starts. The sync adjustment on the Humax caters only for sound ahead. The LG TV caters for both but the adjustment for catching the sound up to the video doesn't go far enough. Max setting is -5 but it would probably need aout -10. LG said TV HDMI's were faulty and replaced set but same thing happens. It is also the same with a Panasonic BlueRay attached via HDMI. It looks like a LG problem, just wanted to rule out the Humax causing it.
 

Black Hole

May contain traces of nut
#6
The video is ahead of sound. If you watch a news broadcaster the lips start moving before the corresponding sound starts.
I'm not saying that's OK, but it is a lot less disturbing than sound before vision.

The sync adjustment on the Humax caters only for sound ahead.
Correct, on the assumption that video takes longer to process than audio (plus the physiological effects as noted).

LG said TV HDMI's were faulty and replaced set but same thing happens.
Then they are idiots. The error is in the processing.

The industry missed a trick by not embedding sync information in the data streams so that everything can be matched up at the presentation device, regardless of the transmission chain.
 
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rollsjohn

New Member
#7
I'm not saying that's OK, but it is a lot less disturbing than sound before vision.

Then they are idiots. The error is in the processing.

The industry missed a trick by not embedding sync information in the data streams so that everything can be matched up at the presentation device, regardless of the transmission chain.
Yes, exactly my thoughts - it sems such a basic thing. Often wondered why film makers used a clapper board but it sycs the sound to vision. No reason why this shouldn't happen electronically with all programme output. Even if I could get my kit in sync I would have to change it every time I changed from Humax to TV's tuner or one of the installed apps and this is just not acceptable.
 
#8
What about trying the boot-settings package which allows you to manually configure the Lip Sync setting - https://hummy.tv/forum/threads/boot-settings-apply-settings-during-boot.7678/. Although this seems to have a slider from 0 to 100, it does seem that you can manually type in a negative number but I haven't tested if it actually works. Worth a try....

BTW, multi channel sound on Freeview HD is in the AAC-LC format. Given very few (if any) AV amps or TVs can handle AAC sound directly, Freeview boxes will re-encode it to Dolby Digital to make it more compatible. So it could be that the delay you are seeing is due to that process, but I've never experienced it on either of mine - the resultant DD audio is always perfectly in sync.
 
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rollsjohn

New Member
#9
What about trying the boot-settings package which allows you to manually configure the Lip Sync setting - https://hummy.tv/forum/threads/boot-settings-apply-settings-during-boot.7678/. Although this seems to have a slider from 0 to 100, it does seem that you can manually type in a negative number but I haven't tested if it actually works. Worth a try....

BTW, multi channel sound on Freeview HD is in the AAC-LC format. Given very few (if any) AV amps or TVs can handle AAC sound directly, Freeview boxes will re-encode it to Dolby Digital to make it more compatible. So it could be that the delay you are seeing is due to that process, but I've never experienced it on either of mine - the resultant DD audio is always perfectly in sync.
renzz, thanks for that. Do you know what the increments are in terms of milliseconds? I'll give it a try.