[opendtv] Re: DD audio bit rates
- From: "John Shutt" <shuttj@xxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 27 Jul 2005 16:29:10 -0400
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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