[vdr] Re: SPDIF on J2 voltage

[Bernd Oefinger <bernd@oefinger.de>]

On Sunday 11 January 2004 21:46, Robert Schneider wrote:

> I have read several postings about the 5V / 0.5V stuff. I running VDR with
> two Rev 1.3 cards with both J2 SPDIF outs directly connected to the Coax
> ins of my Harman Kardon AV-Receiver for years now and I'm facing no
> problems except sometimes loosing audio for a couple of seconds when
> switching channels (annoying but tolarable).
>
> As I'm re-arranging some stuff in my living room, I trying to move to
> bitstreamout using the optical out of my soundcard. While doing that, I
> used a multimeter to measure the voltage of my J2 spdif outs and found
> that the two cards deliver different signals. One card delivers 1.68 V the
> other 3.3V.
>
> Can someone with electronics background shed some light on this for me?
> Isn't the card supposed to deliver 5V?
5V means that the line will be at the level of 5V for a logical "1". A logical 
"0" will produce 0V. To transfer a signal the line toggles at a very high 
frequency (some MHz => this is HF). If the signal is high 50% of the time and 
low 50% of the time you would ideally measure 2.5V when using a simple 
Multimeter.
Depending on the actual hardware, capcitance of cables and the used multimeter 
the measured voltage will vary (which is O.K.).

If you want a deeper understanding:
http://www.epanorama.net/documents/audio/spdif.html

Have fun,
Bernd



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