Digital transmission/storage ensures the signal is not affected no matter how much noise is on the line (well, as long as it can be transmitted at all...)
Now, what I think you mean is that the copper in the cable picks up noise either from the device on the other end or from the surroundings and that has the possibility of affecting the DAC.
Even moderately well designed receiver should be able to galvanically isolate itself from outside sources of noise without having to resort to fiberoptics or wireless. It's just couple of dollars max for extra few components on the board.
For an example possibly familiar in computing circles, Infiniband has easily-accessible counters to record transmission errors. In a properly-built system with hundreds of communication-busy nodes connected with copper, you see remarkably low error rates, even in comparison with the spec (maybe a few a week in my experience).
Infiniband is using extremely isolated and well balanced cables for passive/copper transmission. Also the cable lengths are very short for EDR and beyond (3m-5m is max usable length). For anything longer you need to use fiber cables with embedded converters.
We have a cluster with ~1000 nodes and all generations of Infiniband (DDR/QDR/EDR) equipment, and routing all these copper cables without damaging them is not easy.
The quality of digital tranmsission over copper cables is dependent on the size and clarity of "eye", which is the pattern which two sinusodial signals when run through and oscilloscope. Lower quality cables (HDMI/DP/Coax/etc.) has blurry and small eyes, which increases chances of artifacts and drives the error correction modules harder, while better cables are easier on the both sender and receiver, since they produce lower number of errors to correct.
Trivia: Amphenol / Gore has high speed digital interconnect cables called Eye Opener Plus [0], which also used some of the Infiniband cables that we use.
> Digital transmission/storage ensures the signal is not affected no matter how much noise is on the line (well, as long as it can be transmitted at all...)
There is no such thing as a digital transmission. All signals are analog.
Digital transmission refers to the whole transceiver system, not just the transmission medium. If I can put a "1" in and reliably get a "1" out, it doesn't matter that it was only a 0.9 part way down the wire.
I suppose you need to read up on digital protocols, it is all well handled. If it wasn't there could be no Internet or digital media or even processors or motherboards.
I'm just so tired of all the bullshit where it "Must be a 1 or a 0". That is patently not true. HDMI video, to name one example very relevant to this thread, has no error correction, and bit errors will indeed crop up as the "sparkling" artifacts GGGGGP reported.
Now, what I think you mean is that the copper in the cable picks up noise either from the device on the other end or from the surroundings and that has the possibility of affecting the DAC.
Even moderately well designed receiver should be able to galvanically isolate itself from outside sources of noise without having to resort to fiberoptics or wireless. It's just couple of dollars max for extra few components on the board.