[vdr] Re: AW: Re: AC3 over DVB Nexus-s Card

[Wolfgang Fiesel <fie@iis.fhg.de>]

Hello,

my 2 cent,

Roland Praml wrote:

> > Hi, I am a newby and follow this AC3 over DVB Nexus topic with higher
> > interest. But there is one basic thing I don´t understand: It is a known
> > bug of the DVBs, that the used TI-chip is unable to output a 1:1 signal.
> > One bit can not be output correctly so that AC3 output is said to be
> > technically impossible. Some AC3-decoders seem to have a better error
> > correction so that they still are able to decode AC3, but this is
> > different from case to case. This information is from Hauppauge.
> > So how does the Linux-AC3 output work? Is there a certain work-around
> > for this bug or do the developers simply don´t know about this hardware
> > limitation?
>
> http://www.atsc.org/standards/a_52.pdf
> AFAIK it works like described in annex B

The main reason why AC3 over DVB causes troubles with different DD decoders is
the channel status word bit 1 in the IEC 958 protocol.
See annex B, part 4.1 for details.
At this moment it seems that we can't modify this bit in the TI-chip to
signalize digital data (perhaps there is no control feature implemented).
Therefore some DD decoder regret the "AC-3" data and mute the output.
My Harman Kardon AVR3000 is here more robust and ignores this identification
bit.

Wolfi



>
>
> Roland