GUITAR CABLE CAPACITANCE AND RESONANT FREQUENCY
From: Shootout Guitar Cables UK • Best Guitar Cables Explained
See also: Guitar Cable Capacitance Chart
So far as a passive guitar pickup output signal is concerned, capacitance in a cable can be considered to be part of a tuned circuit (pickup, volume and tone pots, cable and an amplifier, pedal or DI input) which acts upon the high impedance inductive guitar pickup circuit signal like a low pass filter on an EQ that has a resonant frequency bump (gain increase) in the frequency range immediately before the roll off begins i.e it results in significant guitar signal equalisation due to second order low pass filtering.
The input of a tube guitar amplifier, instrument input or buffer pedal typically has a high input impedance of 1 Megaohm (1,000,000 Ohms) which is a low resistance 'load' for weak passive high impedance pickup outputs. Lower input impedances than this will also dull the tone as part of the overall signal circuit with a high pass filtering effect, however then the capacitance will have less relative effect.
Because the pickup signal isn't strong it is also easily affected by interfering electromagnetic signals from other sources when it travels along a cable from the pickups to the amp and so it must be shielded well against this interference, and it is this shielding and signal running along next to each other that creates the distributed capacitance.
The best guitar cables have excellent insulation and shielding to carry away interference to ground, but they can also have low capacitance to avoid as much as possible stripping the signal of high frequencies and lowering the pickup resonant frequency.
The overall design of a cable determines what its capacitance per metre/foot is and this capacitance is measured in guitar cables as picoFarads (pF) per metre, so it is this specification x length that gives us our total capacitance that is what will determine our signal equalisation i.e. the same cable type will sound different at different lengths.
However some pickups are active (powered by a battery) and therefore have a much stronger signal, so cable capacitance does not affect these very much, but many guitarists don't like the way they sound. This is because they interact differently with amplifiers and some pedals, particularly fuzz, treble booster, overdrive and distortion pedals. We will discuss this more in another special section regarding buffers.
The bottom line is that total guitar cable capacitance is the main reason that different guitar cables sound noticeably different to us tone wise (cheap cables are however usually noisy and may also be weak) as the cable is having an equalisation effect on the signal frequencies in the audible frequency range; the higher the capacitance of the cable per unit length and the longer the length of that cable cable the lower the frequency of the resonant bump of the equalisation in the tuned circuit and therefore the more the high frequencies are rolled off.
Cables that are good at rejecting interference and handling noise can also create a lot of capacitance due to this shielding, so the very best cables are very well shielded and so not noisy, but also have low capacitance to avoid dulling the guitar tone too much, the best of both worlds.
So how low a total cable capacitance overall do you need? Well that depends upon where you want your resonant frequency bump to be with the resulting high frequency roll off above, it is subjective.
However, if you have a high capacitance cable you have lost much guitar signal, reduced the resonant peak of your pickup, and you can't put the high frequencies back once gone; but with a low capacitance cable, you have all your high frequencies and harmonics getting to your pedals or amp and you have a tone control with its very own capacitance, and then the tone controls on your pedals and amp, and... you can always use longer cable which is just what some very well known guitarists do!
Here is a DMG Equilibrium EQ mockup of a passive guitar pickup peak resonant frquency of 3.5 kHz presented with very low capacitance including it's own internal capacitance (Fig.1).
Increasing the capacitance by adding cable would move this peak and roll off further and further to the left.
Decreasing the input impedance of the input to amp or pedal would also shift the peak and reduce the resonant frequency height until it was no longer a peak at all leaving just the high end roll off.
Fig.1
Pay no heed to the nonsense whereby cable retailers describe their tone ambiguously with music genre or tone specific terms to describe cables, and ignore the fact that those cables are sold in significantly different lengths which will also change tone! We can easily see through such sales smoke and mirrors for what it really is, a word the Sex Pistols used on an album cover, so never mind it!
Some more considerations:
It is important to remember that the effect of the cables capacitance 'EQ effect' will change the way pedals and amps (when first in line) interact with the signal from the cable from your guitar. Consider again that frequency bump and the roll of above it and then consider a treble booster circuit and how it assists overdrive by exciting amp harmonics and boosting the signal at high frequencies... lots of capacitance pretty much has the opposite of this effect!
Do remember to factor in the length and capacitance of your cable/s from your guitar all the way to your amp, except where you have pedals in between, when it gets more complicated due to pedals with inbuilt buffers and true bypass pedals.
With pedals you need to consider mainly the cable capacitance from guitar to the first pedal in line which is usually fuzz, distortion, overdrive or wah unless you are using true bypass pedals with no buffer in which case you must consider all cables before the first buffer or the amp whichever comes first. The input impedance of your amp is most likely to be 1M Ohm however the pedals may not be. Your dirt pedals will be designed to take the input direct from your guitar with no pedals before and their input impedance will have a big effect. This is one reason why some pedals don't behave well after pedals with buffers or other pedals in general, and why some don't sound good if they are first in line.
Beyond your final pedal the amp input sees the output of the final pedal in the signal chain unless your pedals are off and all true bypass in which case there is no buffer to override the capacitance in the cables on the way to the amp.
Confusing? Not particularly when you understand the basics of input and output impedance and cable capacitance where feeble (but wonderfully dynamic) passive pickup outputs are concerned.
Complicated? With buffered pedals, unbuffered 'true bypass pedals, different pedal input and output impedances and different lengths of different capacitance cables... very much so!
SHOOTOUT! UK guitar cables use very low to ultra low capacitance best quality well shielded cabling... however if you were looking to run 9 metres to a pedal board and then nine metres from the pedal board with no buffering using true bypass and/or vintage pedals... we'd say get a class A buffer pedal and place it after your dirt (overdrive/distortion and especially fuzz) pedals no matter what cables you use.
We hope the above has helped you... yes it is ultimately a bit of a complicated subject (that does seem to be in the nature of guitar tone) but hopefully it need not be confusing.
Also in this guide:
Guitar Cable Length and Signal Loss
Guitar Cable Myths and The Cable Fairy
Guitar Cable Shielding and AC Hum
Braided vs Spiral vs Foil Guitar Cable Shielding
Guitar Cable Microphonics and the Triboelectric Effect
True Bypass Pedals vs Buffered Pedals
Silver Plated Copper Cables and 'Red Plague' Galvanic Corrosion
Copper vs Silver Signal Conductor Guitar Cables
Gold Plated Guitar Cable Jacks and Galvanic Corrosion
Guitar Cables vs Guitar Pedal Board Patch Cables
Analogue Guitar Cables vs WIFI
Low Capacitance vs High Capacitance Guitar Cables
Oxygen Free Copper Guitar Cables
Cheap vs Midrange vs Expensive Guitar Cables
Glued Heat Shrink vs Unglued Heat Shrink Guitar Cables