Why cable capacitance matters, with audio comparisons

[nevershouldhavesoldit]

The recent thread on cable capacitance pushed me to want to hear how it affects our playing. So I fiddled around with multiple cables, styles, picks etc and discovered a major reason not to ignore it. Cable capacitance definitely affects tone - the higher the value, the duller and darker the tone. But it has (at least) one other significant effect. Differences among strings, picks, playing styles etc are more dramatic and better heard with low capacitance cables. Smaller changes in picking position relative to the bridge are more easily heard. Differences among strings are more apparent. For example, differences among lead lines are more apparent when played with different picks and styles. Harder, brigher picks produce sharper attacks and greater definition of individual notes, while smooth soft picks (like the Dunlop 204 and the ProPlec) seem to generate smoother lines that sound a bit more legato and a bit less staccato.

First, I measured the capacitance of several of my cables to find two that were widely disparate. The lowest I could find was 175pF and the highest was 550pF. Then I recorded the same passage through each cable as closely as I could replicate it with 3 different picks on the same guitar recorded directly into a 96/192 M-track DAI and captured in Audacity. Nothing was changed at all except the cables and the picks. The volume and tone pots on the guitar were fully up. I did my best to pick about midway between the end of the fingerboard and the bridge saddle. There is no processing at all, except that I normalized the tracks to keep the average volumes within a dB or two. High frequency peaks are a dB or 2 higher through the low capacitance cable and from the harder brighter picks.

My conclusions are that a low capacitance cable is audibly more responsive to picking and playing style. Subtle tonal dynamics that are not readily apparent through the high capacitance cable are more clearly heard and appreciated through the low one. A low capacitance cable seems a bit more demanding of technical precision, in that it reveals more of the attack of each note. The 204 hides a bit of imprecision in timing and picking stroke while the harder, brighter picks are more revealing. If you want to play a smooth legato line with an acrylic or Lexan pick that has a sharp point or edge, you have to gently stroke the strings and avoid rest strokes. But the same characteristics let those with stellar technique play faster but more precisely controlled lines with the harder and sharper pointed / edged picks. One of the surprising things to me about this comparison is the big difference in the tone of the lowest notes (near the end of the clips). The ending run goes down to a low C on the 7th string (64 Hz).

The softest and smoothest pick was a 2mm Dunlop 204 (polycarbonate), the intermediate was a 3mm Dunlop Jazz Stubby (Lexan) with a sharp point, and the hardest and brightest was a polished acrylic 2mm pick with a precisely beveled edge from Pinter Guitars. The guitar is my Eastman 810CE7 - a 17x3.3" fully carved archtop with a floating KA over a spruce top & maple body, TI JS113s plus a 75 thou Chrome 7th tuned to A. I think the differences are obvious - see if you agree. Here are the short comparison clips:

550pF Dunlop 204 (polycarbonate)



550pF Dunlop Jazz Stubby (Lexan)



550pF Pinter (acrylic)



175pF Dunlop 204 (polycarbonate)



175pF Dunlop Jazz Stubby (Lexan)



175pF Pinter (acrylic)



And here's the head from Groovin' High on my Benedetto Bravo 7 with set KA and TI JS112s plus a 75 thou Chrome through the 175pF cable. The same conditions apply - tone and volume pots wide open, no processing at all (not even normalization on this one) , and as close to identical picking strokes and position as I could get. The differences were more subtle through the 550pF cable, and this post is already too long. But I think the point is clear from these. I was surprised that the Benedetto seems to be even a bit more sensitive to cable capacitance than the 810. See what you think:

204 2mm polycarbonate



Lexan 3mm Dunlop Jazz Stubby



2mm acrylic

[Cunamara]

I was not so rigorous but my own experience with low-cap cables is similar; I use George L's. Going to wireless has brought an even greater sense of transparency, and I like not tripping over the danged cable...

Instrument Cable and Sound – Bill and Becky Wilde Pickups

Macalister Electronics – Guitar Pickup Equivalent Circuits

[GuyBoden]

Excellent deductions as usual.

What about RF Low Impedance cables?

50ohm RF Low Impedance cables have a capacitance of 80 to 100 picofarads per meter.

So, could 50ohm RF Low Impedance cables be used as a Guitar cable?

Maybe, there would be an impedance mismatch problem.

[JazzNote]

How do I measure the capacitance of a cable? The manual of my (very old) analog multimeter tells me that I have to connect it to a 230V outlet in order to measure a capacitor ... but I would not really dare.
TIA

[nevershouldhavesoldit]

How do I measure the capacitance of a cable? The manual of my (very old) analog multimeter tells me that I have to connect it to a 230V outlet in order to measure a capacitor ... but I would not really dare.
TIA

Modern digital multimeters are versatile, accurate, easy to use, and cheap. Just set the dial to capacitance and put the lead clips or probes on the tip and sleeve at one end. Leave the other end open, and don’t touch any part of the plugs or cable while taking the reading. They even automatically set the scale to PF, nuf, of farads to display the significant digits.

I have a $25 Neotech 6000 and an older (but still available) $20 AstroAI that I thought I’d broken. I didn’t, but I also didn’t read the instructions carefully enough Either one is excellent. I was worried that such a cheap device wouldn’t be accurate. But the two read within 2% of each other on everything. I checked them against my ‘50s VTVM and they’re right there on voltage and resistance. So I have confidence in them despite their low prices.

[nevershouldhavesoldit]

What about RF Low Impedance cables?

50ohm RF Low Impedance cables have a capacitance of 80 to 100 picofarads per meter.

So, could 50ohm RF Low Impedance cables be used as a Guitar cable?

RF cable is not a good idea. The shielding is physically much tighter and stiffer than that in audio cable. It’s hard to work with and solder. It’s also not as flexible. Standard RF cable is low impedance but high capacitance. There is low capacitance 50 Ohm RF cable, but it uses a much thicker dielectric (eg foam), it’s bulky, and it’s more fragile inside than audio coax if you crush or bend it..

There are 75 Ohm low cap coax cables like RG59 that run about 20 pF/foot. They’re commonly found in A/V installations like home theater and surveillance networks. You could use RG59U for guitar cables, but it has several drawbacks. It’s designed for permanent installation in stationary settings - it’s not very compliant. Because of its construction, it’s microphonic. If you step on or bend it while it’s in use, it will cause crackling and popping. It’s not very flexible, so it doesn’t lay flat, follow you across the stage easily, or store without a hassle. It also holds kinks and bends.

I wouldn’t use any RF cable for guitar signals. I’ve seen the thin low cap RF cable intended for use inside RF equipment used as interconnects on pedalboards. It works in that application, but I see no advantage to using it in such short lengths.

[GuyBoden]

RF cable is not a good idea. The shielding is physically much tighter and stiffer than that in audio cable. It’s hard to work with and solder. It’s also not as flexible. Standard RF cable is low impedance but high capacitance. There is low capacitance 50 Ohm RF cable, but it uses a much thicker dielectric (eg foam), it’s bulky, and it’s more fragile inside than audio coax if you crush or bend it..

There are 75 Ohm low cap coax cables like RG59 that run about 20 pF/foot. They’re commonly found in A/V installations like home theater and surveillance networks. You could use RG59U for guitar cables, but it has several drawbacks. It’s designed for permanent installation in stationary settings - it’s not very compliant. Because of its construction, it’s microphonic. If you step on or bend it while it’s in use, it will cause crackling and popping. It’s not very flexible, so it doesn’t lay flat, follow you across the stage easily, or store without a hassle. It also holds kinks and bends.

I wouldn’t use any RF cable for guitar signals. I’ve seen the thin low cap RF cable intended for use inside RF equipment used as interconnects on pedalboards. It works in that application, but I see no advantage to using it in such short lengths.

I've got to admit that I made a Guitar cable from 50ohm RF Low Impedance cable more than 15 years ago. It's as you state, inflexible and it’s not very compliant.

Many, many thanks for your excellent advice as always. You're a natural Engineer.

[nevershouldhavesoldit]

It's as you state, inflexible and it’s not very compliant.

When you look at it like that, it could help prepare you to back more than a few vocalists