[vdr] Re: bitstreamout vs. AC3overDVB

["Dr. Werner Fink" <werner@suse.de>]

On Fri, Nov 12, 2004 at 05:48:17PM +0100, hm@seneca.muc.de wrote:
> Dr. Werner Fink <werner@suse.de> wrote:
> > In other word:  I guess that your sound card is slower.
> > Nevertheless you can try to enable VariableIO in the setup of
> > the plugin if you have changed that ... just in case if the
> > your sound card is faster.
> 
> Ouch. This is why a soundcard with an S/PDIF input may be better
> because it can synchronize itself to the sender's clock. Weia. I'll give
> VariableIO a try, thanks for the hint. Sadly enough, the Epia boards have
> no S/PDIF input, at least not the Epia5000. Other Epias may have a CDROM
> S/PDIF input on the mainboard somewhere, I don't know. Anybody? 

For loop through S/P-DIF signal from S/P-DIF out of the DVB-S via
the S/P-DIF in/out of the sound card you're right ... but for
synchronization the sound card with the help of the S/P-DIF in,
also called reference clock or slave mode, or synchronization
depending on the avarage words per second of the data stream
you're wrong for the most sound cards. This because most sound
cards, even some expensive ones, can not be driven in slave mode
nor in word mode.

> I suspect this is where AC3overDVB has its merits because the FF card's
> firmware knows about the sender's clock. Correct?

Exactly.  Beside this my bitstreamout plugin works perfectly for
most AV receivers if the sound card clock is a few ppm faster
then the normal time of the channel.  For other AV receivers
which include the payload of even as error frames marked
nonlinear PCM transport frames, you'll hear an increasing offset.

> 
> It seems I need to unpack my soldering iron over the weekend. A
> simple coax S/PDIF out with just 2 resistors should be okay as a first
> step. The receiver is very likely to decouple its coax S/PDIF input with
> a transformer.

Be warned:  The signal level of the S/P-DIF out of a DVB-S card
is at 5 volt ... you've to use a tranformation (resistors arn't
sufficient to get a coax signal out from TTL) circut and/or
an optical sender accepting a TTL level of 5 volt.
To get it real you may have a look to

    http://www.rf-link.de/AVBoard_Bestellung.txt

to get a solid solution.

> 
> Any hint as to which firmware is currently the best for this job?
> 
> Will AC3overDVB handle non-AC3 sound as well, including MP3 playback
> if I set the MP3 plugin to DVB out?

Hmmm ... I'm currently working on a firmware able to replay PCM,
AC3 from VDR, AC3 and DTS.  At home it works flawless and I'm awaiting
the responce of some testers to make it available for all.
For more information see

   http://www.vdrportal.de/board/thread.php?threadid=21672&sid=

...
   

         Werner

-- 
AC3 loop through sound card http://bitstreamout.sourceforge.net/
Howto http://www.vdr-portal.de/board/thread.php?threadid=1958
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