Interconnect Inductance vs. Capacitance

For a twisted pair design, the capacitance and the inductance are a function of the distance between the conductors relative to their diameters and are somewhat inversely related. The closer the conductors the less inductance and the more capacitance. The further apart, the more inductance and the less capacitance. For instance, a lot of ICs might have a pair of conductors that helix around a core that keeps them at some distance in order to achieve a certain design point (this is just twisted pair from a design point). Similarily, the thickness of the insulation itself can keep the conductors separated at some distance in a twisted pair that does not have a 'core'. The capacitance is also related to the type of dielectric used (or more specifically, the effective relative permitivity of the dielectric that the conductors experience). There are other cable geometries that are used that will tend to push the impedances one way or another. In general, all of the impedances (resistance, capacitance, inductance) scale linearly with the length of cable so shorter is better if you want to minimize impedances.

It's probably easiest to try to get the vendor's specs on what impedance a given cable exhibits - if they've bothered to measure them. Measuring inductance and capacitance typically requires a pretty good (expensive) piece of equipment. Low capacitance and low inductance are both desirable, but since you usually hurt one to help the other, going two far in either direction tends to be a mistake. However, I agree with Almarg that capacitance is a bigger factor for ICs while inductance (and resistance) is generally a bigger factor for speaker cables due to the differences in the amount of current involved between the two (e.g. harder for a low current system to charge a capacitance while harder for a high current system to overcome inductance).

Other things that are reputed to affect the "sound" of cabling are the purity of the conductor (e.g. OFC (99.99%), UPOCC (99.9999%), solid conductors supposedly better than stranded conductors, the type of conductor (copper, silver, silver coated copper), effective cross section of total conductors (more cross section, less DC resistance), diameter of individual insulated conductors (smaller gauge wires show less variation in internal impedance with frequency (due to skin effect, DC travels through the entire conductor - higher frequencies move to the outsides of the conductor - so some vendors will say you should have, for instance, a number of smaller gauge conductors (say 8 x 21 AWG) rather than one large conductor (say 1 x 12 AWG) for speaker cables), surface of conductor (smooth/polished is better), the type of dielectric (actual physics here that affects capacitance), the geometry of the conductors within the cable , the mechanical stability of the conductors (e.g. damping and isolation), how well the connector or wire makes contact with the terminals (e.g. type of plating on connectors, type of metals in connectors, surfaces of connectors, contact points of connectors, contact enhancement treatments, oxidation on connectors, vibrations in connectors, etc.), shielding from RFI and EM radiation (more important on ICs due to low voltages and currents and subsequent application of the noise through your amplifier), and various types of conditionings like cryogenic freezing. However, there is great controversy over which, if any, of these types of things has an impact on the 'sound' or whether "great" sound can be achieved with a 'budget' cable.

To be honest, most cables spec's are not going to be a problem from an electrical standpoint - unless perhaps your amp is sensitive to highly capacitive loads (most are designed not to be) or you are running at lot more than say 8 feet of cable. And most of the cable specs are not going to tell you something that will indicate whether it sounds better or worst to you in your system. Even if the cable were to have characteristics that introduce frequency distortion - perhaps you like attenuated highs on your ICs because your gear is bright for instance.

However, most audio folks say that they hear differences between different cable's sounds. Most differences in cables' sounds are 'subtle' and perhaps a matter of taste. To me, it seems to be a bit of a hit or miss operation if you are just looking at 'spec's. It's not clear what measured parameters are important to the "sound" and there's a lot of marketing hype about various other characteristics that are hard to substantiate. If you can actually audition some cables and you like one better than the other - and you feel that the difference in cost justifies the improvement, then go for it - though this could lead to a potentially un-ending cable upgrade path if you have unlimited time and resources. The next best source is likely to be discussion forums of other folks experiences with various cables on various types of equipment (particularly the ones where they decided to go from cable x to cable y).

Keep in mind that some cables reportedly require some period of time to settle into how they will ultimately sound. If you believe in breakin (another controversy), the periods typically indicated for this transition tend to be on the order of a few days to a week or two of active (24x7) use, depending on a number of factors - though most likely related to the type of dielectric. If you are trying to compare two cables - that is also a bit of a dicey operation. Try to keep all other variables constant. Same gear, same room, same speaker placement, same relative placement of listener to the speakers. It may take you some time of listening before you decide that a particular sound is to your liking - what might sound like more definition at first might end up seeming harsh after a while. So it may take more than just flipping back and forth a few times to get to a lasting impression of whether you really like one sound versus the other. Also keep in mind that your listening room may have a much larger effect on the sound of your system than the cables so if that's out of control - perhaps you're better off focusing on that first before you start trying to 'tune in' your cables. Another rule of thumb quoted would be to not spend more than about 10-20% of your system's cost on cabling. If you are spending more that on cabling, you might be better off buying better gear than better cables.

Not much help here, but a lot of things to consider perhaps. From what I'm seeing, seems like perhaps a bit too focused on the capacitance vs inductance issue as the title suggests. Try measuring more with your ears than your impedance meter. However, if you are interested in some more of the technical side, this might be helpful - http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/Analog.html

I just got a set of Blue Jean cable IC's to run between my $4000 preamp and $5500 amps. The LC-1 cost me $38 shipped for a 5 foot set. Do the math folks....they sound very good and I will let you know more once they are burned in more.

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.