Ask Lemmy

Another audio professional here. For line level analog audio (it's different for guitar pickups and turntable cartridges) it doesn't matter much at all unless we're talking long cable runs (several tens of meters and more) or some badly designed equipment that can't handle high capacitance cables (eg I've had crappy amps going into oscillations with certain speaker cables). What matters is shielding (in noisy EM environments) and reliable connectors.

Digital audio is a different kettle of fish, but it's amazing what you can get away with when runs are a few meters or less. Consumer-grade equipment almost never has 75 ohm connectors for coax S/PDIF and no consumer S/PDIF cable is really 75 ohms. RCA connectors cannot be 75 ohms due to their geometry and BNC is a rare beast (I really had to go out of my way to set up proper 75 ohm cabling for digital audio in my home, and still am not sure the BNC connectors I use are actually 75 ohms).

I should also mention to all non-audio pros that you can't measure a cable's or a connector's characteristic impedance with a simple multimeter. 50, 75 and 110 ohm cables/connectors will all show milliohms on a multimeter and are all fine for audio frequencies. Characteristic impedance only plays role at high frequencies—MHz, not kHz range and when we need to impedance match the whole transmission line to avoid signal reflections.

I would be more worried about channel crosstalk when using a multi-core cable where conductors are not individually shielded as is the case with USB cables, but even 30 dB separation is probably fine for casual music listening.