[BC] DTV Audio Levels

[Urban, Brian L]

That's all well and good in theory Richard.  In practice, the TV guys tell me a different story.  Lip sync is a real problem for them with digital TV.  A few milliseconds becomes VERY obvious VERY quickly, especially when the audio leads the video, which can easily happen when doing post production where the audio and video paths are separate and have different processing delays.  It can quickly become a real mess.

Splitting the audio out of the bitstream is fairly easy (as has been pointed out); working on the audio and getting it back into the bitstream in proper sync isn't so easy.

Somewhere I read an article that specified the points where lip sync became obvious and annoying-if I find it, I'll post the numbers.  All I remember is being amazed at how small the time interval was.

--
Brian Urban
Chief Operator
KUT Radio
The University of Texas at Austin
TEL 512-471-1085

On 6/16/09 9:49 AM, "RichardBJohnson at comcast.net" <RichardBJohnson at comcast.net> wrote:

I don't think it would take more than a few milliseconds to process the audio. There shouldn't be an resynchronization problems because synchronized audio was delivered with the video. Synchronization problems come into play when one has multiple paths for both the video and the audio. The TV station already has synchronized audio available from the network. Extracting digital audio from the composite signal is a trivial operation, with the maximum latency determined by the dictionary length in the compression. This is all "realtime" as far as audio is concerned, consuming a few tens of audio frequency cycles, maximum. Actual signal processing is instantaneous when related to slow varying information like audio.

Cheers,
Richard B. Johnson
Book: http://www.AbominableFirebug.com/

----- Original Message -----
From: "Cowboy" <curt at spam-o-matic.net>

On Tuesday 16 June 2009 09:53 am, Jim Tonne wrote:

>  And, Richard, how would you do that without losing
>  "lip sync"?  This has been pointed out before; the video
>  would have to be delayed the same amount of time.

 And that was the whole point !
 Lip sync is not something we deal with in radio, but it
 is a very big deal in TV.