[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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