[opendtv] Re: DD audio bit rates
- From: "John Willkie" <JohnWillkie@xxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 27 Jul 2005 14:20:33 -0700
John;
I'm sorry, I should have been more specific. What A/52 gives in bit rates,
A/53 takes back in audio system constraints, and adds a few new
requirements.
John Willkie
----- Original Message -----
From: "John Shutt" <shuttj@xxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Wednesday, July 27, 2005 1:29 PM
Subject: [opendtv] Re: DD audio bit rates
> John,
>
> We fix dialnorm. The audio is dialnormed by PBS so our decoder maintains
> that level. We do have Wohler audio meters that meter the level of the
AC-3
> encoded audio so we are fairly sure of consistent audio levels.
>
> Looking at A/52b, I see bitrates up to 640Kbps for each service are
allowed.
> I don't see anything that says the maximum bitrate for 2.0 audio is 192
> Kbps. Also, if you have a main channel and a second language channel,
each
> is encoded separately and allowed to be up to 640K each.
>
> John Shutt
>
> ----- Original Message -----
> From: "John Willkie" <JohnWillkie@xxxxxxxxxxxxx>
>
>
> > 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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>
>
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