[linux-dvb] Re: AC3 via S-PDIF

[Ralf Bauer <RBauer@quark.de>]

The datarate is 3.072 Mbit/s for 48kHz sampling rate, which is too much for
either serial or parallel port. You really need something which is connected
to your system bus.

But there are solution for USB-port:
http://www.soundkartenkatalog.de/deu/c28.html
http://www.opcode.com/products/datport/
http://www.musiklabor.de/soundkarten_spdif.htm
http://ezone.techno.cz/electrobook/audiomidiusb.html

There's a nice collection of S-PDIF related links here:
http://www-md.e-technik.uni-rostock.de/~fs60/SPDIF.htm

Ralf.

-----Original Message-----
From: Klaus Schmidinger [mailto:Klaus.Schmidinger@cadsoft.de] 
Sent: Tuesday, June 19, 2001 18:10
To: linux-dvb@linuxtv.org
Subject: [linux-dvb] AC3 via S-PDIF


Maybe somebody with deeper knowledge about this can help me out here:

I understand that an AC3 decoder accepts the digital data through either a
coaxial or optical input line. That line (or the protocol?) is specified as
"S-PDIF". This is a unidirectional link and there is no handshake.

Since the hardware on the DVB-S card apparently can't be used to send the
AC3 data stream to an external AC3 decoder (at least that's what the driver
developers wrote here on the list, IIRC), and I don't want to install a
sound card in my VDR box just because of the S-PDIF interface (it's not
because of the costs, it's because such a card would occupy one of my
valuable PCI slots ;-) I was wondering what is actually necessary to
implement an S-PDIF interface. The electrical circuitry appears to be pretty
trivial (see for instance "elektor" 7/8 2000, page 37). And the actual data
I guess would consist mainly of the AC3 data stream as received from the
transponder. The question now is: does that data have to be modified in any
way (like adding a ninth bit, repackaging or stunts like that), or is it
just to be sent "as is"?

What I am thinking of would be a small electrical interface connected to the
serial or parallel interface. The data could then just be sent to 
the respective device and we would not need any special sound card driver
(and we would also not have to install a sound card :-)

Is this idea in any way feasible - or am I missing something important here?
Would the bandwidth of the serial or parallel interface be enough for the
AC3 data stream?

I do admit that my knowledge of S-PDIF is next to zero - but I hope to
change that...

Klaus
-- 
_______________________________________________________________

Klaus Schmidinger                       Phone: +49-8635-6989-10
CadSoft Computer GmbH                   Fax:   +49-8635-6989-40
Hofmark 2                               Email:   kls@cadsoft.de
D-84568 Pleiskirchen, Germany           URL:     www.cadsoft.de
_______________________________________________________________


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