Why do digital cables sound different?

Expensive Digital cables sound different because you sit lower in your chair when listening to them. This is because your wallet is empty.

A digital waveform can be very badly distorted, as viewed by the eye, but a well designed line receiver will still properly distinguish ones from zeros. Furthermore, if an error is made, or even a group of errors, perhaps due to some unrelated power glitch or scratch on the CD, a data stream with error correction encoding (like a CD) will still be recovered exactly. Them is the facts.

Drubin...So let's turn this question over to the psychologists. Electrical engineering has no explanation.

Spatialking...A digital waveform does not represent the information being communicated (a "one" or a "zero"). The waveform is sampled at some specific instant of time to determine if it is above or below some threshold. Where the signal goes in between sample times is completely irrelevant. All that matters is that the sample time be chosen so that it is well away from leading and trailing edges of the waveform where the signal level is changing rapidly and might be misread.

In a complex digital system that I worked on (Missile guidance) we had dozens of analog signals being sampled and digitized, and many digital signals being used to generate pulses of power (amperes) to control things like gimbals. All in the space of a 9 inch sphere, so you can imagine the electrical noise environment! By very careful selection of sampling times and signal sequences it all worked fine, although you would never have thought it possible if you looked at the raw analog signals. The bottom line is that a sampled data system does not exist except at the sample times.

Ar_t...One interesting experience in my career as a systems engineer on Submarine-Launched Ballistic Missiles was a visit aboard a 20 year old boat to evaluate the ability of the existing wiring from tube to fire control (as much as 300 feet) to transmit digital data at the higher bandwidth to be used by a new system. We injected pulses at one end and looked at them with a scope at the other end. My God! Were they ever distorted. All kinds of spikes and overshoots. But, and here is the point, the information transfer over the wires using those sorry-looking pulses was flawlwss.

You have described how the digital waveforms are distorted by improper impedance, stub terminations, etc. but it is still unclear how an analog wareform reconstructed from digital information could be affected by the shape of the digital pulses.

Ar_t...The system I described does have a separate "clock" line. Actually there are three lines, One, Zero, Strobe.

1, 0, 1 is a one.
0, 1, 1 is a zero
Any other set is invalid.
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Wire properties can certainly affect digital pulse characteristics. But, up to the point where a data "one" can be misinterpreted as a "zero" pulse characteristics don't affect the information which goes into the D/A converter.
So I don't find it "mysterious" at all that various cables sound the same. The mystery is why some folk think they sound different.

Shadorne...If a cable causes a pulse risetime anomaly (such as a spike) it will happen for every pulse. All will be delayed or trigered early by the same amount, so jitter is not the result.