[mythtv-users] HDMI_SPDIF directly to reciever

[Johan]

On Sat, 2008-07-05 at 08:44 +0200, Johan wrote:
> On Fri, 2008-07-04 at 22:16 -0700, Alen Edwards wrote:
> > 
> > 
> > James wrote: 
> > > Roo wrote:
> > >   
> > > > 2008/7/5 James Lockie <bjlockie at lockie.ca>:
> > > > 
> > > >   
> > > >     
> > > > > There is 0 volts on the RCA.
> > > > > 
> > > > > Why do I get sound if there is a zero volt signal?
> > > > > I tested my voltmeter on a battery to verify it works.
> > > > >     
> > > > >       
> > > > James,
> > > > 
> > > > If your voltmeter is on a DC range and the output is bipolar, +0.5V
> > > > and -0.5V then that will "average" out to 0V. This is irrespective of
> > > > the data travelling over the spdif as it is Manchester Coded.
> > > > 
> > > > Try an AC range on the voltmeter if you have one.
> > > >   
> > > >     
> > > AC is 3 something.
> > > So if my receiver expects 5V and it is getting less, am I hurting it?
> > > 
> > >   
> > > > HTH,
> > > > 
> > > > Roo.
> > > > ___________________
> > > 
> > If you are getting 0 DC and 3AC, I am surprised.  I would expect it to
> > be the other way around (0AC and 2-3DC).  No matter, less it good and
> > your receiver is probably saying it can take anything up to 5 volts
> > and it can probably take much less, like maybe .1 volts.  Some people
> > on this list have said their equipment works all the way to .025
> > volts.  I would double check your numbers and readings then try it.
> > 
> > 
> > Allen
> > 
> > _
> Summarizing:
> 
> the signal is digital manchester coded and probably bipolar, so will not
> contain a DC component.
> It's sampling rate is up to 96kHz, to high for most multimeters. 
> Multimeters do not measure peak values, but only average (they are even
> "calibrated" in RMS (root MEAN Square). So you will never know what peak
> voltages are actually present. 
> Only way to be sure is to use an oscilloscope.
> 
> know it does not help, but clarifies a shortfall in the measuring
> technique..
> 

This article might be interesting. I also mentions that the data is not
bipols, but merely capacitive coupled (or using a transformer), removing
a DC component. This will then only work using the "manchester like"
coding, as standard digital signals may remain too long at a "1" level
to be passed through a cap or a transformer.

http://www.epanorama.net/documents/audio/spdif.html


> Johan
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