Interconnect Inductance vs. Capacitance

For an interconnect, there is no question you want low capacitance or the treble begins to roll off, coupled with group delay. The group delay can have a significant effect on the subjective impression of speed and dynamics of much of the music spectrum. But inductance is another matter. Inductance in an interconnect is really only relevant in that it affects the characteristic impedance of the cable. In an ideal world the characteristic impedance of an interconnect would be at, or slightly above, the output impedance of the upstream component. If the characteristic impedance of the cable is below the output impedance of the upstream component then phase errors can get audible, particularly in the bass, and is a major cause of the belief that interconnects can be system dependent. If the characteristic impedance of the cable is too far above the output impedance of the upstream component then it can act as an antenna and pick up noise and fine detail will be lost or obscured. With no standard for output impedance for audio components then one of the challenges for a designer of interconnects is how to minimize the problems of impedance mismatches. Some claim to have effectively eliminated this problem with their designs.

Redkiwi -- Interesting post. But I think it should be pointed out that many, and I would venture to say most, people with relevant technical knowledge (who are not manufacturers of certain high-end cables) would disagree with some of your statements about characteristic impedance.

Characteristic impedance, being part of what are called "transmission line effects," is (at least for typical interconnect lengths) generally considered to be utterly inapplicable to audio frequencies. Note that I limited the statements in my first post above to cables carrying analog audio, not digital signals, video, or rf.

And I am at a loss to see how, even if there were some significance at audio frequencies, phase errors in the bass would result from impedance mismatch.

I do agree that pickup of high frequency noise might, in the hypothetical case of a cable that is both unshielded and unbalanced, be influenced by impedance mismatch between cable and source component. However, noise rejection is best addressed, and is usually addressed, by quality shielding and, in the case of balanced interconnections, by common mode rejection.

Regards,
-- Al

Hi Al. I should disclose that I am a cable designer and so you can accuse me of being a snake oil salesman now (insert smiley face here - I am taking a shot at myself, not at you). But responding to your point. One of the problems in science is that when experimenting you need to assume certain variables are not relevant in order to observe the impacts of an experiment on what you believe to be relevant. You cannot screen out all other variables all of the time. This leads the electrical engineering field to have certain beliefs - such as the one you have expressed, that many issues in transmission theory don't apply at audio frequencies for short cables. That is fine for the EE that simply wants to make something work. To optimize a system, it is not good enough. In pushing the envelope to develop better audio cables many/most designers I know revisit what the typical EE assumes away as irrelevant, and tests whether indeed it makes a difference. A good case in point these days is skin effect. Most EEs I know that are not working in high end audio will assume skin effect is an irrelevant issue for audio frequencies, and yet there are many of us designing cables who have found otherwise, and many designs are specifically targeted at dealing with skin effect in various ways today. Another example is in the area of digital cables, where one of the smartest designers I know, Dan Lavry, has at least once stated his belief that using a correct impedance cable is not relevant for short lengths of a meter or so, yet most digital cable designers have found otherwise. Using absolute beliefs is a necessary part of life, or we would be hopelessly confused. But testing for how those absolutes are really shades of gray is necessary for some innovations to occur. When I design, I just try different things. When I hear an effect, I search for a theory that might explain it. Armed with a possible theory, I then conduct an experiment to see if in fact using the theory to predict the outcome of different iterations proves to be useful. If it does then it adds to the mix of theories I use to optimize a cable's performance. In the vast majority of cases the theories that I use are accepted theories, just not normally considered to be relevant at audio frequencies for short cables. I suspect we are wandering far from the OP's interests, my apologies to the OP.

A gap between theory and reality is that there is no theory (that I am aware of) explaining how human being would perceive various specs in high end audio. I have never seen any EE courses relating human perception and technical specs in any length of details, even after my 3 EE degrees.

Let me give an example to illustrate my point. I had a DIY preamp project recently. I used 0.68uF for the output coupling caps. Since my power amp has an input impedance of 500K, it yields 0.5Hz 3db cut-off freq. Then I changed the output caps to 10X value; i.e., 6.8uF. The 3dB freq. is now 0.05Hz. Interestingly, I can hear better bass. A couple friends can hear that too.

I am not sure that there is any theory that can explain it!

Back to ICs. Redkiwi, your postings are interesting. Can you tell us the specs of your ICs after you improved the skin effect?

Thanks.

My point is that there often is theory. It is just that we don't always consider it relevant to the particular context, and it turns out it is.

In the case of the larger cap - it is possible that more bass extension reduced group delay, but it is also possible the larger cap released energy more slowly, smearing the signal slightly and giving the impression of greater weight. One therefore needs to experiment to confirm what is happening.

I wasn't referring so much to my interconnects when referring to skin effect ideas that are floating around. Some of the ones I find interesting are those being talked about by Supra and LessLoss, for example. With cable experiments I very rarely use any measuring equipment other than the ears of a listening panel so specs aren't possible.