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Auddio sync with HDMI and analog out


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In my kitchen I have a cable box connected to my TV via HDMI and I have the analog audio from the cable box connected to a C4 matrix amp that drives two zones in the kitchen, plus some adjacent areas.  If I have the TV sound on as well as the amp while watching TV I can hear an echo, so the video is slightly out of sync with the audio. I am hypothesizing that the analog audio may be slightly ahead of the HDMI audio.

I am feeding the analog audio out of this TV back into my C4 amp so I have two audio sources - which I need for other sources as this is a Roku TV which I use for streaming service like Netflix.  When it comes to cable, which of the two audio sources from my cable box is most properly synced?  I would think it is the audio on the HDMI as I assume that the analog audio coming directly from the cable box is slightly ahead of the video due to HDMI/HDCP processing, is it not?  So I should use the TV out as the audio source on the matrix amp rather than the analog out from the cable box, correct?

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40 minutes ago, zaphod said:

So I should use the TV out as the audio source on the matrix amp rather than the analog out from the cable box, correct?

It's almost certainly the TV introducing the slight delay as it processes the HDMI signal (and auto syncs the audio) - but is there a reason you want the tv audio to begin with? If so, yes feed the TV back.

How this works in programming can be a bit more difficult - as it depends on setup etc (ie is the cable box used in other rooms would be the starting question)

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The reason I want to feed the Tv back is that the TV is the AV source for streaming services as it is a Roku TV. But I don’t really need that for other AV sources like the cable TV, but I was playing around with the different sources. (Edit inserted cable before TV in the previous sentence)

But if it is the TV introducing that delay then wouldn’t it also introduce the same delay into the video?  So then don’t you want that delay to maintain the most accurate sync with the video.  When I use the TV feed back as the audio source for the amp it is in sync with the TV speaker. 

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My point being, the few MS delay you see now is likely only noticeable due to the echo - so if you don't use the TV speakers, chances are you'd never have noticed the minor sync issue. Of course this tends to different by person, as well as attention/focus on it but you (a human one would presume) are likely to be unable to tell the audio is out of sync when watching and hearing someone talk with as much as a 20-30 ms difference - generally 10ms or less is considered completely impossible to notice for the humans to begin with - but you can notice an echo or 'hollow' sound due to two identical audio streams at a delay in some cases with a delay as minimal as HALF a ms)


Indeed, sound travels as what, about 1/3 of a meter per millisecond? so at an average of 3 meters (approx 10f) away you've just inserted a 9ms delay already - your brain washes that away no matter how hard you try. This is also why surround systems have a distance setting for speakers, and why it's important to set those...because now you could have a 3ms sync issue between the same sound wave coming out of more than one location ... and that you CAN notice (in fact, it's how that 'fun' little 'cathedral' sound setting that Yammy seems to insist on having works)

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All TVs have processing delay on the video path (HDMI in to screen), from a minimum of about 5ms (really good Game mode) up to about 100 ms (all the 3d processing modes turned on).

The audio path inside the TV will be properly matched to whatever the internal video delay is.  This allows the TV speaker to maintain proper sync regardless of what modes you have enabled.  The TV audio output (dig / analog) is generally also delay matched in the same way.  Some high end TVs also have a +- delta delay you can add to the TV audio out jacks to compensate for any delay in external speakers.  Some really cheap TVs don't delay match the TV audio outputs or have other issues, but that is rare.

So in your case the easiest solution is to try putting the TV in GAME mode.


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9 minutes ago, zaphod said:

Thanks @videostorm.  So are you saying that the TV audio out will be most properly synced to the video rather than the cable box audio out?  And put the TV in Game Mode.

Yes, TV audio out is synced to video on the screen.  Putting the TV in game mode is a way to reduce the delay of the TV if you need to use centralized speakers for TV audio (since the difference in delay will be minimized).

IMO, TV speakers or TV audio out should always be used INSTEAD of centralized audio for TV viewing.  This is both for delay matching and directionality.  However, you have to work with what you have so find the best solution for you of course.

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