Comparing the tone of three different "boutique" cables

[ggunn]

See, some ears can be trusted.

That's not what this means. If there really is a difference in the audible frequency spectrum of signal passed through this particular cable (which has yet to be proved; what we have so far here is correlation, not causation) it just means that not every difference perceived is necessarily imagined. We knew that already.

 

[fdeck]

It isn't a meaningful concept. Anyway, I thought we were measuring the frequency response of the cable. What does the instrument have to do with it? I'm confused by that.

How a cable affects the output of a passive electric bass depends on the circuit characteristics of the bass.

The purpose may not be to measure the pup, but in this test you are doing just that. The signal isn't generated by the pup. It's generated by the generator. The pup changes it's characteristics in an apparently unknown way.

I was assuming a relatively simplistic model of a pup as a voltage source in series with an inductor. In that case, adding a second voltage source in series with the first makes sense. It does neglect the capacitance between windings, and the method of an external coil would address that situation. As a control, you could measure the output of the pickup open-circuit, and then loaded by a cable.

 

[seanm]

Incidentally, I worked it out with BK to figure out how to use their tester for cable capacitance, so I have those data points now. I'm working on a big comparison chart with all the data: resistance, capacitance, f, THD, noise, etc.

Can you post how you tested the capacitance?

Aside from the Zerocap cable which hasn't arrived yet, the lowest capacitance is the Elixir (10.8 pF per foot) followed by the Planet Waves (15.9 pF per foot). The highest is the Analysis Plus (49.7 pF /foot) and the Evidence Audio (37.4 pF /foot).

Thanks for the numbers! This explains why my spice models where not working right. I had the capacitance way too high!

With the numbers for the planet waves cable, I am now closer to your pickup graph. The bump now happens at about 4kHz. Better than the 1.8k I was getting before

 

[bongomania]

The capacitance test is with the cable coiled fairly tightly, to minimize pickup of EMF; and one tester lead to the center wire of one end of the cable, the other tester lead to the shield wire of the same end of the cable; the far end of the cable is unterminated, open air.

 

[KJung]

See, some ears can be trusted.

Very few have ever said that the capacitance of cables, combined with cable length and a passive instrument would not impact the upper treble response of an instrument. This is well known.

However, what Bongo is showing is what is also well known, that capacitance has a zero correlation with price of cable.

However, capacitance with a passive bass and a reasonably short cable length (under 20 feet) seems to have a minimal impact in the real world, and only seems to emerge in listening tests with cables at the extreme end of the continuum (i.e., George L's, which are super low capacitance and do sound a touch brighter than most cables, and the Analysis Plus and Monster 'Bass' cables, which are super high capacitance, and do choke off the upper treble a bit to my ear). With active instruments, the whole issue becomes somewhat trivial and so subtle as to be relatively meaningless for the vast majority of players.

Of course, for many bassists who don't have a lot of upper treble much less lower treble in their tone, it is a bit of a moot point even with passive instruments. For guitarists, it is more of an issue across a wide range of players and tone goals.

IMO and lots of IME!

 

[A440Hz]

It seems to me you're measuring the effect that the combination of the pup and the cable are having on the pink noise. The pup will most certainly not be transparent. There will be all manner of phase and frequency effects just from that. The output of the pup should be the base line. Try taking an additional trace off of the node between the pup and the cable.

I'll bet there's more difference between pre-pup and post-pup than there is between post-pup and post-cable.

This still isn't the best method, but it's closer, I think. The best way would be to put a complex signal into a metal (ferrous) diaphragm and vibrate it in the magnetic field of the pup. Measure the output of the pup as the base line and compare the output of the cable to that base line. Not sure how to physically achieve that, but if can be done it'd really tell you something definitive.

Assuming that the pickup and cable are linear, time-invariant systems (LTI, as the jargon goes), it doesn't matter what order they are placed or whether or not you take a measurement before or after the pickup--the cable is the variable here, and by changing the cables and re-running the sweep, bongo is measuring apples to apples.

Of course, neither a pickup nor a cable is perfectly linear, but for small signals, they're close enough for Jazz. Or Precision. Whichever you prefer.

EDIT: I forgot to mention that someone out there has a device just like you describe--an electromagnetic generator that you place over the pickup to measure specs. The generator coil is relatively low-impedance and wide-bandwidth. Can't find this device on the google right now. My google fu is failing me. Also, I think it was in the neighborhood of $900. Ow.

 

[thepontif]

I understand it's apples to apples when comparing one cable to another, and I know that's the idea with the experiment. But it should be made clear that if the PU is part of the thing being measured, the charactizations we see on these graphs don't reflect the characteristics of the cables themselves. We do get to see how one cable is different from the other, though. We just never see an absolute picture of what the cable itself is doing to the signal.

 

[A440Hz]

Um, you did understand what I was saying about cascading LTI systems, right? Because as long as the LTI system (in this case, the pickup) is applied to all cables equally, it's still apples to apples, even with the pickup in place, and no matter where you measure it.

 

[thepontif]

Yes, it gives you an apples to apples comparison of one cable to the next, which I agreed with already. It's just that the apple consists of a pickup and a cable. Not just a cable.

All I'm saying is that these graphs don't give an ABSOLUTE characterization of the frequency response of these cables. It gives us a characterizations of a circuit consisting of a cable connected to a pickup. Change the cable and see how the characteristics change, but you're still looking at the difference between (cable A+pickup)-(Cable B+Pickup). Not, "what are Cable A's characteristics?" in an absolute sense.

 

[ggunn]

Yes, it gives you an apples to apples comparison of one cable to the next, which I agreed with already. It's just that the apple consists of a pickup and a cable. Not just a cable.

All I'm saying is that these graphs don't give an ABSOLUTE characterization of the frequency response of these cables. It gives us a characterizations of a circuit consisting of a cable connected to a pickup. Change the cable and see how the characteristics change, but you're still looking at the difference between (cable A+pickup)-(Cable B+Pickup). Not, "what are Cable A's characteristics?" in an absolute sense.

But it's the cable+pickup system that we are concerned with and how that system changes (or doesn't change) when you swap cables. This is an applications problem.

 

[scotch]

Yes, it gives you an apples to apples comparison of one cable to the next, which I agreed with already. It's just that the apple consists of a pickup and a cable. Not just a cable.

All I'm saying is that these graphs don't give an ABSOLUTE characterization of the frequency response of these cables. It gives us a characterizations of a circuit consisting of a cable connected to a pickup. Change the cable and see how the characteristics change, but you're still looking at the difference between (cable A+pickup)-(Cable B+Pickup). Not, "what are Cable A's characteristics?" in an absolute sense.

Hmm,... I'm trying to find the motivation behind your perspective. There's seems to be acknowledgement of limited value to Bongo's test, but at the same time you allude to the fact that it's not an applicable test for use as a 'bassist' at the same time. I'm confused. I could also be reading you totally wrong!

Do you think a test with just the cables, and no loading from the pickup, would be better? Or do you want more "real world" variables added in? Or are you just a little biased against this type of testing in general?

Not loaded questions, I promise! Just trying to get a sense of where you are coming from. Given that you are an electrical engineer in the MI industry, it seems that your' perspective carries a little more weight.

 

[A440Hz]

Yes, it gives you an apples to apples comparison of one cable to the next, which I agreed with already. It's just that the apple consists of a pickup and a cable. Not just a cable.

All I'm saying is that these graphs don't give an ABSOLUTE characterization of the frequency response of these cables. It gives us a characterizations of a circuit consisting of a cable connected to a pickup. Change the cable and see how the characteristics change, but you're still looking at the difference between (cable A+pickup)-(Cable B+Pickup). Not, "what are Cable A's characteristics?" in an absolute sense.

I understand now what you're saying. It's a relative vs. absolute thing.

Given the fact that bongo has done "flat" cable testing and with the pickup in series, I'd say he's done the "in the absolute sense" as far as he can take it with his measurement system.

 

[thepontif]

I get it. It's a fine test. I'm only pointing out, for those who just want to know what cable to think about buying and don't get or care about science, that what they should be concerned with in making their choice is not any ONE frequency curve itself, but the differences between them. You're not seeing the "curves" of the cables...only a set of curves that reflect differences between the cables.

It still seems that a comparison of the pink noise through just the pup and the pink noise through the combination of pup and cable (both into the same load) would paint a more nearly accurate picture of what the cable itself is doing.

 

[ggunn]

I get it. It's a fine test. I'm only pointing out, for those who just want to know what cable to think about buying and don't get or care about science, that what they should be concerned with in making their choice is not any ONE frequency curve itself, but the differences between them. You're not seeing the "curves" of the cables...only a set of curves that reflect differences between the cables.

It still seems that a comparison of the pink noise through just the pup and the pink noise through the combination of pup and cable (both into the same load) would paint a more nearly accurate picture of what the cable itself is doing.

But if all the cables do the same thing, why do we care what that is?

The question that bongo has chosen to address is if different cables have different electrical characteristics that can be tied to their sounding different. It's relative; what a cable does in an absolute sense is a totally different question. It's not like a cable is optional. Yeah, I know, there's wireless, but that's a whole nother can o' worms.

 

[bongomania]

OK, a small update--I just ordered the ADC option/upgrade for my Focusrite ISA One. This will achieve two things: One, the ISA has a switchable low-impedance option on the DI input, so that will solve the "z in problem". Two, the ISA's ADC is far, far higher quality than the Presonus unit, with much wider bandwidth, lower noise, and flatter response. I may still have to use the Presonus for the output of the pink noise signal, but a significant portion of the test mechanism will have been improved, reducing its effect on the test results.

I won't be able to make any progress on these tests over the next couple of days as I'm attending some all-day IPC certification classes, but perhaps by Friday I may have the ADC installed, the complete pickup/vol-tone pots harness wired up, and I can begin experimenting with piezo diaphragms for transmitting signals into the pickup.

 

[Nic.]

Wow it took ages to read through all the pages that popped up when I wasn't looking.

Anyway, I might have missed something, but why not test coiled cables? I know a lot of people swear they destroy the tone. Do they? I've been using mine without noticing any harmful side effects to my sound but I've always just attributed that to my active bass and imperfect ears.

Since a few people have made the "best cable for metal" joke, here's the answer:

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Not enough spikes.

 

[fdeck]

We just never see an absolute picture of what the cable itself is doing to the signal.

It's capacitating the signal.

You are correct. The pickup and the cable are both part of a circuit. Both are doing something to the signal. The capacitance of the cable is a load on the pickup, but the effect of that load depends on the characteristics of the pickup.

My suggestion is that if the cable and pickup are thought of as being components of a circuit -- or even more precisely components of an electromechanical system -- then a lot of the confusion about what is being tested goes away.

 

[fdeck]

I get it. It's a fine test. I'm only pointing out, for those who just want to know what cable to think about buying and don't get or care about science, that what they should be concerned with in making their choice is not any ONE frequency curve itself, but the differences between them. You're not seeing the "curves" of the cables...only a set of curves that reflect differences between the cables.

It still seems that a comparison of the pink noise through just the pup and the pink noise through the combination of pup and cable (both into the same load) would paint a more nearly accurate picture of what the cable itself is doing.

Agreed. This would show how the capacitance of the cable is loading the pup.

 

[bongomania]

why not test coiled cables? I know a lot of people swear they destroy the tone. Do they?

Good point! I'll get one.

 

[Nic.]

Good point! I'll get one.

Awesome. Hopefully that proves to my guitarist that he's just being picky and delusional