Co-ax SPDIF digital out
 

"Jim Lesurf" wrote in message



I've cheerfully used 50 Ohm co-ax and also 'randomly chosen'
phono-coax for short lengths, and it seemed fine. However this was
for lengths of 1 metre, and with Meridian DACs at the receiving end.
These seem to be good at rejecting various problems. Hence I suppose
it is possible that some combinations of 'odd' cable and
transmitter/receiver would be problematic.

I've used a piece of zip cord with RCA plugs soldered at each end. I've read
a report of a guy who used two wetted fingers to make the connection between
a digital source and a digital converter.

Co-ax SPDIF digital out
 

In article , Arny Krueger
wrote:
"Jim Lesurf" wrote in message



I've cheerfully used 50 Ohm co-ax and also 'randomly chosen'
phono-coax for short lengths, and it seemed fine. However this was for
lengths of 1 metre, and with Meridian DACs at the receiving end. These
seem to be good at rejecting various problems. Hence I suppose it is
possible that some combinations of 'odd' cable and
transmitter/receiver would be problematic.

I've used a piece of zip cord with RCA plugs soldered at each end. I've
read a report of a guy who used two wetted fingers to make the
connection between a digital source and a digital converter.

Well, fingers *are* "digital"... ;-

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Co-ax SPDIF digital out
 

In article , Arny Krueger
wrote:
"Jim Lesurf" wrote in message



I've cheerfully used 50 Ohm co-ax and also 'randomly chosen'
phono-coax for short lengths, and it seemed fine. However this was for
lengths of 1 metre, and with Meridian DACs at the receiving end. These
seem to be good at rejecting various problems. Hence I suppose it is
possible that some combinations of 'odd' cable and
transmitter/receiver would be problematic.

I've used a piece of zip cord with RCA plugs soldered at each end. I've
read a report of a guy who used two wetted fingers to make the
connection between a digital source and a digital converter.

Well, fingers *are* "digital"... ;-

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Co-ax SPDIF digital out
 

In article ,
Arny Krueger wrote:
I've used a piece of zip cord with RCA plugs soldered at each end. I've
read a report of a guy who used two wetted fingers to make the
connection between a digital source and a digital converter.

Yup - all this about cable and plug impedance is so much bull**** on the
short lengths normally encountered here.

--
*24 hours in a day ... 24 beers in a case ... coincidence? *

Dave Plowman London SW 12
RIP Acorn

Co-ax SPDIF digital out
 

In article ,
Arny Krueger wrote:
I've used a piece of zip cord with RCA plugs soldered at each end. I've
read a report of a guy who used two wetted fingers to make the
connection between a digital source and a digital converter.

Yup - all this about cable and plug impedance is so much bull**** on the
short lengths normally encountered here.

--
*24 hours in a day ... 24 beers in a case ... coincidence? *

Dave Plowman London SW 12
RIP Acorn

Co-ax SPDIF digital out
 

"Jim Lesurf" wrote in message
...
In article , "Bedouin"
In principle, losing some of the 'squareness' of the edges should not
matter if the receiver can still read the data OK. Although there may be a
possible effect of 'data induced jitter' of the kind that Julian Dunn and
others have discussed in the past. In practice I have my doubts about this
being a serious problem, though, in most casts.

It was the introduction of Jitter due to the rounding of the signal that I
was thinking about.

I'm not sure what part of the "square wave" a DAC typically detects. If it
is a zero crossing point which in many ways seems the most sensible then
loss of the high frequencies will have little effect, if it works on a point
away from the zero crossing then loss of the high frequencies could be very
significant.

Co-ax SPDIF digital out
 

"Jim Lesurf" wrote in message
...
In article , "Bedouin"
In principle, losing some of the 'squareness' of the edges should not
matter if the receiver can still read the data OK. Although there may be a
possible effect of 'data induced jitter' of the kind that Julian Dunn and
others have discussed in the past. In practice I have my doubts about this
being a serious problem, though, in most casts.

It was the introduction of Jitter due to the rounding of the signal that I
was thinking about.

I'm not sure what part of the "square wave" a DAC typically detects. If it
is a zero crossing point which in many ways seems the most sensible then
loss of the high frequencies will have little effect, if it works on a point
away from the zero crossing then loss of the high frequencies could be very
significant.

Co-ax SPDIF digital out
 

On Mon, 01 Dec 2003 23:20:58 GMT
"Bedouin" wrote:


I'm not sure what part of the "square wave" a DAC typically detects. If it
is a zero crossing point which in many ways seems the most sensible then
loss of the high frequencies will have little effect, if it works on a point
away from the zero crossing then loss of the high frequencies could be very
significant.

If the jitter is considered noise, and thus phaseless, then it may have no effect on the reconstruction at all, as 16 bits are needed to form a sample and the jitter may very well totally cancel itself out in that time (plus there plenty of time for a PLL to smooth things over there AIUI.

TBH though I recon USB audio would be a decent alternative to all this unidirectional crap ;-)

at least USB allows bi-directional communication and has enough bandwidth to allow the fetching of a few more bits if any get eaten on the way to their target. Granted the signal may *possibly* get so totally destroyed that it can never be reconstructed in time, even with retries, but the probabilities of this get vanishingly small on USB2.0 devices...

--
Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux

Do not meddle in the affairs of Dragons, for you are tasty and good with ketchup.

Co-ax SPDIF digital out
 

On Mon, 01 Dec 2003 23:20:58 GMT
"Bedouin" wrote:


I'm not sure what part of the "square wave" a DAC typically detects. If it
is a zero crossing point which in many ways seems the most sensible then
loss of the high frequencies will have little effect, if it works on a point
away from the zero crossing then loss of the high frequencies could be very
significant.

If the jitter is considered noise, and thus phaseless, then it may have no effect on the reconstruction at all, as 16 bits are needed to form a sample and the jitter may very well totally cancel itself out in that time (plus there plenty of time for a PLL to smooth things over there AIUI.

TBH though I recon USB audio would be a decent alternative to all this unidirectional crap ;-)

at least USB allows bi-directional communication and has enough bandwidth to allow the fetching of a few more bits if any get eaten on the way to their target. Granted the signal may *possibly* get so totally destroyed that it can never be reconstructed in time, even with retries, but the probabilities of this get vanishingly small on USB2.0 devices...

--
Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux

Do not meddle in the affairs of Dragons, for you are tasty and good with ketchup.

Co-ax SPDIF digital out
 

"Bedouin" wrote in message

"Jim Lesurf" wrote in message
...
In article ,
"Bedouin" In principle, losing some of the 'squareness' of the edges
should not matter if the receiver can still read the data OK.
Although there may be a possible effect of 'data induced jitter' of
the kind that Julian Dunn and others have discussed in the past. In
practice I have my doubts about this being a serious problem,
though, in most casts.

It was the introduction of Jitter due to the rounding of the signal
that I was thinking about.

I'm not sure what part of the "square wave" a DAC typically detects.

I've probed real-world SP/DIF lines and found that there typically is no
square wave on a SP/DIF line. More often than not, it most resembles a
modulated sine wave. This is because the output of most SP/DIF coax outputs
is routed through a transformer with controlled losses at high frequencies.
The low-pass characteristic is there for so the device passes DFCC part 15.
Signal detection is based on something like a Schmidt trigger doing level
high-hyseterisis level detection.

This scheme is of course sensitive to noise pickup. Any jitter that is added
at this point is supposed to be removed further on down the line.

If it is a zero crossing point which in many ways seems the most
sensible then loss of the high frequencies will have little effect,
if it works on a point away from the zero crossing then loss of the
high frequencies could be very significant.

Here's a spec sheet for a relevant part:

http://www.sc-elec.demon.co.uk/cs8411.pdf