Do I need an expensive digital cable?

@audio-b-dog 

"Well, it was a 50 ohm cable not made for digital" isn’t scientific enough. The digital signal did pass through it, and digits are digits, and the digits are double checked to be correct

Unless I am completely mistaken, your CD connects to your DAC using S/PDIF over copper wires.  S/PDIF defines the physical connection and the data link layer.  These are the lowest two layers of the seven-layer OSI network model, and the data link layer is the lowest layer of the IP network model.

There is no requirement for the data link layer to detect or correct data errors.  That is typically done by higher level protocols operating at higher levels in the network stack.  Your assertion that "the digits are double checked to be correct" is not true for S/PDIF, any more than it is for I2S.

As others have stated, all cables carry analogue signals, so there really is no such thing as a digital cable.  The confusion arises because of the characteristic impedance required.  S/PDIF specifies 75 Ohms whereas most RCA cables are nominally 50 Ohms.  All that happens when impedances mismatch is that more of the signal gets reflected back into the cable at termination points, and less gets through.  This makes it harder to determine when the signal has transitioned between on and off, or vice versa.  In turn, that makes it harder to synchronise a clock over the cable.

It does not stop a digital signal being retrieved, which is what you observed.  It does not mean that all the digits are received correctly, so the sound quality may well vary, which is what you report.

You really should read up a bit more on networking, and what the various layers do.

@richardbrand 

Thank you for your detailed response. Does your argument also apply to digital 70 ohm cables? Back to our initial discussion. Will a "better" digital cable, better quality of wire and better quality of shielding, perform better than an inexpensive cable with low-grade copper wire and low-grade sheilding? There seems to be a number of people on each side of this argument. I will get back to my test between the $14 digital cable and $249 digital cable when I have time and energy. I did not really give them a good test by listening to them for a longer time. 

@richardbrand 

I worked in the computer industry for 20 years and I was educated on a lot of aspects of computing, including networking. I left the industry in 2,000, so I'm sure a lot has changed.

I worked at Hewlett Packard selling to the defense industry, Navy and Air Force. I remember in the early 90's when one of my customers asked me, "What's this new 802.3 thing. I need to use it to communicate with another base." I'm sure you know that was the beginning of the internet. I took classes on network packets and what was invovled in a network packet.

Again, I'm sure it's different in audio. But, I have no interest in studying this stuff anymore. I'm writing a novel which requires a lot of research on ancient history, so that's pretty much what I read now. But I do appreciate people like yuou who can bottom line things for me.

Im trying to figure out if I’m the crazy one or if 90% of audiophiles are full of **** or just gullible.

@kumizi  Well, as I mentioned several cable companies allow for returns and you’re only out return shipping in most cases if you don’t hear a significant improvement, so what are you afraid of?  Then again, you can’t hear any differences between a $100 and $5000 speaker cable so may just be a waste of time anyway, and it’s much easier to just bury your head in the sand so I’ll give you that. 🙄

A small part of me envies folks who harbor unquestioned certainties. I can see how it makes life simpler.