High End Cables Audio: The Chain and Its Signals

Quick answer / TL;DR: High end cables audio covers four jobs with four sets of figures. The speaker run carries power into 4 to 8 ohms, so its gauge and termination dominate. The line-level interconnect carries a voltage into a high impedance input, so capacitance and shielding dominate. The digital link must hold its characteristic impedance – 75 ohm for coaxial S/PDIF, 110 ohm for AES – or the reflections corrupt the stream. The phono lead carries a millivolt signal whose high-frequency response depends on the cable capacitance against the cartridge loading.

High end cables audio is not one product: a system uses at least four kinds, and the physics of each is different enough that a figure which matters at the speaker terminal is irrelevant at the digital input. The chain runs from the source to the driver, and each link carries a different kind of signal – a tiny voltage, a standard-impedance digital stream, a low-impedance power output – so the cable's job changes at every stage.

This is the chain view: the four cable jobs and the physics of each, the figures that matter at each stage, and where in the chain the money actually changes the signal.

Four Jobs, Four Sets of Figures

The chain's four links carry different signals, and each link's cable is judged on the figures its signal is sensitive to. The speaker run carries the amplifier's power output into a 4 or 8 ohm load, so the series resistance and the termination are the figures that move. The line-level interconnect carries a volt or two into an input of 10 to 100 kilo-ohms, so the capacitance becomes a filter and the shielding becomes the noise floor. The digital link carries a stream at a defined characteristic impedance, so geometry and impedance tolerance decide whether the data arrives. The phono lead carries a few millivolts from a cartridge whose response depends on the load capacitance it sees.

The table is the chain read link by link, and the reading is that no single cable figure serves all four. A heavy gauge that helps the speaker run adds nothing at the digital link, where the impedance tolerance is the whole job; a low-capacitance interconnect that suits a valve preamp is wasted on a speaker terminal. Buying one construction across the chain is buying one figure for four problems.

The Speaker Run and the Line Interconnect

The speaker run and the line interconnect are the two links most systems get wrong, in opposite directions. At the speaker terminal the voltage is high and the impedance low, so capacitance is almost irrelevant and the resistance in series with the driver is everything – the gauge and the joints. At the line-level input the voltage is low and the impedance high, so the same capacitance now forms a filter with the source impedance, and the shielding decides how much hum and radio frequency reaches the input stage. The two links want different builds, and a cable chosen for one is rarely right for the other.

Capacitance, and where it stops being a rounding error

Capacitance is the figure that separates the two links, and its importance scales with the impedance it works against. A few hundred picofarads across a 4 ohm load is a corner frequency far above the audio band; the same capacitance feeding a 100 kilo-ohm input puts the corner inside it. That is why the interconnect's capacitance per foot is quoted in the specification and the speaker cable's rarely is, and why a long interconnect into a high-impedance input is the one place a cable change is most likely to be measurable.

The Digital Link, and the Phono Lead

The digital link is judged by a figure that has nothing to do with the audio band: the characteristic impedance, 75 ohms for coaxial S/PDIF and 110 ohms for AES on twisted pair. The cable must hold that impedance along its length, and the connectors and the terminations must not introduce a discontinuity, because a mismatch reflects the edge and the receiver works harder to recover the clock. The phono lead is the opposite extreme – a millivolt signal from a cartridge whose high-frequency response depends on the total capacitance it sees, typically a few hundred picofarads including the arm wiring, the cable and the preamp input. There the cable's capacitance is part of the cartridge's load, and the grounding is part of the noise floor.

The millivolt link, and the loading figure

The phono link's figure is the total load capacitance, and the cable is one of three contributors to it. The cartridge's specification states the range it expects; the arm's internal wiring, the cable and the preamp's input capacitance add up against that range. A cable with a high capacitance per foot on a long run pushes the total past the range and tilts the top octave, while a low-capacitance lead keeps the total inside it. That is a cable figure that changes the signal, and it is the one the phono link is bought on – not the conductor metal.

The chain is stocked link by link – the speaker runs by gauge and termination, the interconnects by capacitance and shielding, the digital links at 75 and 110 ohm, the phono leads by capacitance and grounding; the catalog lists the figures each part is specified at.

Real-World Applications

The valve system with a high-impedance input: the interconnect's capacitance is the figure that changes the top octave, and the speaker run is bought on gauge alone. The streaming setup with a coaxial digital link: the 75 ohm impedance and the connector continuity are the whole purchase, and the conductor metal is not the figure. The turntable rebuild: the phono lead's capacitance counted against the cartridge's stated load, and the ground wire treated as part of the same job. In each the chain is four problems, and the money goes where the link's own figures are the ones the signal sees.

Related reading: The line-level link in full: high end interconnects — high-end-interconnects

Related reading: The millivolt link and its loading: high end phono cable — high-end-phono-cable

Frequently Asked Questions

What cables does a high end audio system need?

Four jobs: the speaker runs from the amplifier to the drivers, the line-level interconnects between sources and the preamp or amplifier, the digital link from a transport or streamer, and the phono lead from a turntable. Each carries a different signal, so each is judged on different figures – gauge at the speaker, capacitance and shielding at line level, characteristic impedance at digital, capacitance and grounding at phono.

Should I spend more on interconnects or speaker cables?

Spend where the figures the system can resolve are failing. A long run to a 4 ohm speaker makes the speaker gauge the priority, and a high-impedance valve input makes the interconnect capacitance the priority. A digital link needs the correct impedance rather than an expensive construction. There is no single order that fits every system, which is why the chain is assessed link by link.

Does cable capacitance matter for speakers?

Very little at the speaker terminal, where the impedance is 4 to 8 ohms and a few hundred picofarads forms a corner far above the audio band. The same capacitance matters much more at a line-level input, where the impedance is tens of kilo-ohms, and it matters most on a phono lead, where it is part of the cartridge's specified load. The figure is real; its importance depends on the impedance it works against.

What is the right impedance for a digital audio cable?

75 ohms for coaxial S/PDIF and 110 ohms for AES on twisted pair. The cable, the connectors and the terminations must hold that figure along the run, because a mismatch reflects the signal edge and makes the receiver work harder to recover the clock. Digital cables are bought on impedance tolerance and connector quality rather than on conductor metal.

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