DeserTBoB wrote:

As someone with over 20 years in the telecommunications field, the
last half being digital, I'll end this by saying that the ONLY
parameter that directly affects digital is level...period...as long as
the cables are within specified length. Over that length, lump
constants start rounding leading edges, but it STILL doesn't
matter...as long as the threshhold is reached for a 1, -1 or 0, who
cares what the leading edge looks like??

Yes, but you're also working with well-designed equipment that accurately
regenerates clock from a noisy signal.

You would not BELIEVE how badly-designed the input stages on some of the
equipment out there is. And it's not just a Japanese manufacturer whose
name begins with "PAN" and ends with "SONIC" either. There is a lot of
high dollar D/A boxes out there which are shockingly sensitive to the
quality of received clock.

And it is just getting worse with the shift to 96 ksamp/sec rates, too.

It's not hard to design this stuff properly, but it does require test
equipment that can display spectra of received clocks, etc. And it
requires engineers to actually pay attention to what they are doing.

It's certainly a lot better than it was 20 years ago in the PCM 1630
days, but there's still a lot of trash out there.

I did an experiment similar to the "coathanger" experiment years ago,
using SO cord as a patch cord on a 110 ohm digital patch trunk at the
DS-1 level. Results, NO change. Of course, with analog, things would
have gotten nasty on a 600 or 135 ohm balanced pair if this went for
any distance, especially at group frequencies (60-108 KHz) or above,
but digital didn't care at the DS-1 and E-1 levels, 1.544 and 2.048
Kb/s respectively. At 45 MB/s (DS-3), then things went to coax and
loss was indeed a factor. The cure? Crank the gain up a little on
the transmit side, and I got error free performance on the
receive...even using SO cord at the DS-3 level. Would I use this as
an in-service thing? Hell no...110 ohm balanced patch cords (same
things as used for 600 ohm voice, actually) and RG-187 coax with WECO
connectors ONLY. But, it proved my point...digital's either "good" or
it's "bad," there are no varying impairments like in analog, just
varying bit error rates.

If Bell Labs designed the S-PDIF standards, you'd be able to do this
with audio gear too. With some audio gear you still can. Don't try
it with the Wadia.

I swear, I need to go into the snake oil business. There's too much
money to take away from fools who obviously don't need it.

The whole audio business is snake oil. You're making people think
there is an orchestra behind those two black boxes, when there really
isn't any such thing. There's some pride in that.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."