Why do digital coax cables matter?

Jitter is measurable, correct?

certainly

"Will a cable of some determinate length not add some measurable, repeatable, non-arbitrary amount of jitter within a particular range of measurement, regardless of any jitter coming from the source component?"

Yes, assuming the signal is repeatable.

"Are there any cable manufacturers that measure and publish jitter specifications for each of their different cable products and cable lengths?"

I cannot think of any cable manufacturers that can afford a $150K analyzer from Agilent that it takes to measure this. Even JA of Stereophile with his latest and greatest AP system cannot measure it.

The other thing you must understand is that a lot of the jitter problem in cables is caused by imperfect receivers in the DAC, not the cable itself. If you put an analyzer at the end of the cable instead of the DAC receiver, everything changes. You lose half of the effects.

Steve N.

Ones and zeroes doe not exist in real life; it is all analogue signals, interpreted as numbers.
You would like thee signals to be the only one on the cable, and you want them unaltered, so interpretation is flawless.
If the cable picks up or rejcts other signals, noise, it could upset f.i. feedback loops in amp stages, giving distortion.
It the signals that represent the numers themselves are distorted, interpretation and timind can suffer; this is jitter.
So a cable could do a few things wrong, and then there is impedance match which I frankly do not quite understand.

Because the SPDIF digital signal is NOT a matter of the presence or absence of a signal (standard binary). It is the transition from the falling square wave to the next and transition across the top of square wave to the next drop that comprises the binary data. Additionally it is out of sequence to give error correction a fighting chance to keep things straight. You can only see this on an oscilloscope that is rated out to 100 mHz. The rise and fall times are in the nanosecond range and cable quality and correct impedance are key to good sound reproduction. Maybe more so than analog interconnects.

My two cents.

Walt D'Ascenzo

I use Ethernet CAT-5e wire with quality RCA jacks. It sounded as good as if not slightly better than a $500 Nordost digital cable. I figured that a cable that can pass a 350mhz computer digital signal would work for audio digital connections.

Steve, thanks very much for your comments and insights.

My one comment in response is in regard to:

10-06-12: Audioengr
"Characteristic impedance different than 75 ohm can be very good, as Al mentioned, if it is better match for given system."

Sure, but I would sell that system and get one that meets the specs so I dont have to try to find a wacked-out cable that matches it.

The problem as I see it, in at least most cases, is that there is no practical way for the consumer to know what the transport's output impedance or the DAC's input impedance is. Even JA's measurements don't address those parameters, at least in the reviews I've looked at. And, if I recall correctly, the tolerance defined by the S/PDIF standard is a very loose one, something like +/- 20 ohms or +/- 20%.

Also, as indicated in your paper:

I have never seen impedance control on any Transport or DAC circuit board. Occasionally, the wiring from the circuit board to the connector is impedance-controlled, but this is the exception, not the rule.

It all seems to me to add up to a very hit or miss situation, and even more so given that another key parameter, the risetime and falltime of the transport's output signal, is also usually unspecified, and widely variable (e.g., 25 ns or so in many cases, per your paper; 3 ns or less in some cases, per your statement above).

10-06-12: Dura
... and then there is impedance match which I frankly do not quite understand.

See Steve's paper, linked to above, which explains it all nicely.

Regards,
-- Al