The 75 ohm impedance rating of a digital cable does NOT mean that its resistance is 75 ohms. It's resistance for any reasonable length is likely to be well under one ohm, and insignificant in relation to the source and load impedances of the two components it is connecting (which presumably are 75 ohms). If you were to measure the resistance between the two ends of a digital cable with a multimeter (either between the center pins of the two rca connectors, or between the shield connections/ground shells of the two rca connectors), the multimeter would indicate that very low value.

What the 75 ohm cable impedance refers to is what is called "characteristic impedance" which is a concept that only comes into play at frequencies that are much higher than audio frequencies, such as radio frequencies, and the high frequency spectral components of digital audio signals.

The idea is that the characteristic impedance should match the source and load impedances, or else reflection effects will result at those high frequencies, resulting in waveform distortion, which in turn can result in increased jitter and even mis-clocking and data corruption or loss if severe enough.

The characteristic impedance of a cable, btw, is to a close approximation equal to the square root of (its inductance per unit length divided by its capacitance per unit length). Therefore it is independent of length.

Regards,

-- Al

What the 75 ohm cable impedance refers to is what is called "characteristic impedance" which is a concept that only comes into play at frequencies that are much higher than audio frequencies, such as radio frequencies, and the high frequency spectral components of digital audio signals.

The idea is that the characteristic impedance should match the source and load impedances, or else reflection effects will result at those high frequencies, resulting in waveform distortion, which in turn can result in increased jitter and even mis-clocking and data corruption or loss if severe enough.

The characteristic impedance of a cable, btw, is to a close approximation equal to the square root of (its inductance per unit length divided by its capacitance per unit length). Therefore it is independent of length.

Regards,

-- Al