Adventures with Clock Cables

@daveteauk 

ChatGPT for the answer

Great question. The “75 ohms” rating of a BNC digital audio (or video) cable refers to the cable’s characteristic impedance, not its DC electrical resistance.

Here’s what that means:

• Characteristic Impedance (75 Ω):
  This is a property of the cable as a transmission line, determined by the ratio of its inductance and capacitance per unit length (geometry + dielectric material). It describes how signals “see” the cable when traveling at high frequencies (like digital audio or clock signals).
• Why It Matters for Clock Signals:
  A digital word clock is a high-frequency square wave (essentially RF-like in behavior). To keep the edges clean and avoid reflections, the cable’s impedance must match the source and load. In audio/video and word clock systems, that standard impedance is 75 Ω.
• If Mismatched:
  If you used a 50 Ω or random coax instead of 75 Ω, the mismatch would cause signal reflections along the cable. That can smear clock edges, increase jitter, and degrade timing accuracy—something you don’t want in a high-end digital audio system.
• DC Resistance vs. Characteristic Impedance:
  If you measured the cable with a multimeter, you might see less than 1 Ω end-to-end. That’s just copper resistance. The 75 Ω rating is not a resistance you can measure with a multimeter; it only appears when the cable is carrying high-frequency signals.

So, in short: the 75 ohms rating ensures proper transmission of fast clock edges with minimal distortion and reflection.

@jfrmusic,

Thanks, it is good to have some concensus that you also find that the higher ranges of Shunyata clock cables are not automatically superior, when noise filters are employed which is not always benefits for some systems, i guess.

How do you connect the N20 to your MSB, did you also try the Shunyata AES or spdif cable between the units or via MSB optical?

Thanks

Digital cable that sounds better in one system can sound worse in another.  It all comes to better matching of characteristic impedance.  Price of the cable doesn't guarantee that.  Cable might have exact 75ohm, but DAC (or source) could be less or more.
Characteristic impedance is very difficult to measure, since inductance and capacitance in the cable are "distributed" so it is necessary to try cable in the system.  For that reason I wouldn't pay any attention to reviews (other than built quality and shielding)

@justubes2 

I use the AES/XLR to connect the Aurender to the MSB. Originally had a Blue Jeans cable. I upgraded to a DH Labs. Tried a Shunyata Alpha but preferred the sound of the DH Labs. Also tried the DH Labs Silver Reference but found it too bright. 

While I have NOT done a ton of experimentation with clock cables, I’ll share an anecdote from my experience. I used to run a dCS Rossini and Rossini clock. The pair came with some clock cables. At one point I wondered if I could even hear a difference if I tried something different and I ordered some Geistnote cables. My memory is a little fuzzy, so I may have this reversed, but IIRC I ordered some 0.5m cables. I tried them and I convinced myself that maybe I heard a difference and maybe I preferred the Geistnote to the stock cables it came with. But then I found some discussion suggesting that clock cables should be no shorter than 1.5m. These are really inexpensive cables, on the order of $40 at the time, so I said “why not” and ordered 2m cables of the same model. They were a revelation. There was no “maybe I hear a difference.” It was a dramatic step change. The specific improvement was a sharpening of the focus around the environment. That is, while already, in the right recordings, I was transported to the venue and you could hear the room, those details were more resolved and specific. Anyway, that’s my anecdote about just a change in clock cable length.