[opendtv] Re: DD audio bit rates
- From: "John Willkie" <JohnWillkie@xxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 27 Jul 2005 13:12:28 -0700
by doing what you are doing, you are avoiding at least two of the many
pitfalls with AC-3:
1.) no glitches when the STB goes from 2.0 to 5.1 and vice versa.
Sometimes when this happens, 5.1 channels go through 2 channels, with the
resulting volume 2.5 times higher than the surrounding material; and the
output channels can be unpredictable: with the powered channels being in the
rear, or on one side, or ...
2) you insure -- I hope -- the correct audio levels at the transmisison
point.
How do you do dialnorm? Have you considered the Linear Acoustics box?
John Willkie
----- Original Message -----
From: "John Shutt" <shuttj@xxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Wednesday, July 27, 2005 9:24 AM
Subject: [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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