[opendtv] Re: DD audio bit rates

According to our Dolby Model DP569 AC-3 audio encoder manual, the entire 
bitrate is allocated to the selected audio mode, so I would say the 2.0 has 
"higher quality" than the 5.1.

The Dolby manual says that for mono anything from (all numbers in Kbps) 56 
up to 640 is valid, and 96 is recommend, for 2.0 stereo anything from 112 up 
to 640 is valid and 192 is recommended, and for 5.1 anything from 384 up to 
640 is valid, with 448 recommended.  But as I said, we heard that some early 
generation STBs didn't like anything other than 384, so that is what we run. 
I seem to recall a recent recommendation from Dolby for ATSC stations to 
increase their 5.1 audio rates to at least 512, but I think interoperability 
issues with legacy receivers were never addressed.

For our HD service we use a Dolby Model DP564 AC-3 decoder to decode the 
AC-3 audio from PBS and synthesize discrete 5.1 if the incoming audio is 
2.0, or simply decode the 5.1 to 6 discreet channels if the incoming program 
is encoded 5.1.  The 6 channels of audio then go through our Evertz Mini 
Master Control switcher into the DP569 to be encoded into AC-3 3/2L (5.1) at 
384.  The encoded AC-3 bitstream is then passed to the Tandberg MPEG encoder 
which simply encapsulates it into the transport stream.

We do this with the HD because the thought was that our stand alone Dolby 
decoder would probably do a better job of creating 5.1 out of 2.0 material 
than the built-in Dolby chip in most STBs.  Whether it actually does or not 
is an issue for audiophiles.

John

----- Original Message ----- 
From: "John Golitsis" <john@xxxxxxxxxxxxxxxxxx>


> Thanks John.  Is the 2.0 of a higher quality, or just stuffed with
> lots of nulls?


 
 
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