Why do digital coax cables matter?

Geoffkait 8-30-2017
... so what’s the diff?

The difference is the frequencies that are involved, Geoff, which bring completely different effects into play. Such as the one that is explained in the paper by Steve N. of Empirical Audio that was referenced earlier in the thread, which explains the rationale for 1.5 meter digital cables. That rationale having no relevance whatsoever to analog audio signals, since it involves the effects of signal reflections that result from impedance mismatches at RF frequencies on timing jitter at the point of D/A conversion. Surely you realize that cable effects can be dependent on frequency, especially when both the frequencies and the application are vastly different? If you don’t, any further debate would be pointless, and I’m not going to engage in any.

Also, your last sentence represents a complete misreading of what I have said. I absolutely did not say, and have never said in this thread or any other, that length differences in analog cables won’t be audible. In fact in many other threads, such as this one in which you’ve participated very recently, I’ve said that they certainly can be audible. I have said, however, that in general the shorter an analog cable is the better, assuming the goal is for the signal to be conveyed in as accurate a manner as possible (i.e., for the sonic effects of the cable to be minimized).

Feel free to have the last word, even if it involves asserting that something I have neither said nor implied is incorrect. To others who may be interested in the subject, I would commend the excellent posts earlier in the thread by Kijanki, AudioEngr (Steve N. of Empirical Audio), and others, as well as my own posts.

Regards,
-- Al

Sorry Al, don’t buy it. You get an E for Effort. I won’t point out your name dropping. You apparently haven’t had the opportunity to try the Shun Mook Orignal Cable Jacket or the Highwire Cable Wrap, both of which improve the sound of *analog* cables by, you guessed it, addressing the cable reflections. I know what you're thinking, "But, but that disobeys the laws of science!" 😀

cheers

People would be much better off if they believed in too much rather than too little. - PT Barnum

I won't pretend to know much of the scientific facts about cables and I maybe over simplifying this, but doesn't cable inductance have a large effect on a cables sound. Inductance is affected by length, isn't it???

Mr_m, yes, inductance and most other cable parameters are proportional to length, including resistance, capacitance, the resistance rise at high frequencies caused by skin effect, the effects of dielectric absorption, and propagation delay.

In the case of analog cables, inductance is most likely to be audibly significant in speaker cable applications, especially if the impedance of the speaker is low at high frequencies (as it generally is in the case of electrostatic speakers), and/or if the cable length is long, and/or if the particular cable has relatively high inductance per unit length. The impedance presented by an inductance is proportional to frequency, and therefore in the upper treble region may become an audibly significant fraction of the impedance of the speaker in those situations.

Inductance (as well as resistance) will usually be unimportant in the case of line-level analog interconnects, since the corresponding impedances will be vastly smaller than the input impedance of the component receiving the signal. In that application capacitance will often be important, particularly if the output impedance of the component providing the signal is high.

In the case of digital cables, inductance is one of the key determinants of what is called "characteristic impedance," which for coaxial S/PDIF is nominally the 75 ohm figure you are probably used to seeing mentioned, and for AES/EBU is nominally the 110 ohm figure you are probably used to seeing mentioned. The characteristic impedance of a cable is NOT proportional to length. However at the RF frequencies which comprise digital audio signals the less than perfect impedance match that will inevitably exist to some degree between the cable’s characteristic impedance and the nominally 75 or 110 ohm impedances of the connected components will result in some fraction of the signal energy reflecting and re-reflecting back and forth along the cable. The arrival of those reflections and re-reflections at the DAC will result in some degree of distortion of the signal waveform as received by the DAC, which may or may not ultimately affect timing jitter at the point of D/A conversion, depending on the arrival times and also on the design of the particular DAC. And those arrival times will be dependent on the length of the cable as well as on the propagation velocity of the particular cable. That is explained well in the paper by Steve N. of Empirical Audio that was linked to earlier.

Regards,
-- Al

The more things change the more they stay the same. This whole discussion is a rehash of what was said in the early days of this thread five years ago. In fact, it’s a rehash of the cable controversy that started what, 40 years ago? All you need is zip cord or something like that. And technical types were claiming the laws of physics were being broken back then, too. "There are only 3 things that can affect cable performance, resistance, capacitance and inductance." Yeah, right.