Raz59
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Post by Raz59 on Oct 8, 2010 7:30:34 GMT -5
In order to properly test the effect of components, one must test each variable at a time while keeping all other variables constant. A person on another forum was wondering about a way to remove the "human" variable out of the test, to which I suggested the following: - Solder a pickup straight to the guitar's output jack;
- Plug the guitar into a loop pedal and record whatever you want;
- Then connect the output of that pedal to the input of a potentiometer (volume pot);
- The caps would be between that pot and another one (tone pot);
- The output of the volume pot would go either straight to a tube amp or straight to the PC and saved into a lossless audio file format.
Essentially, the pedal would take the role of the guitar. A constant and consistent signal would be sent to a 500k audio-taper potentiometer; a second pot would serve as the tone control, and the capacitor to test would be placed in alligator clips. A wire-o-gram for demonstrative purposes: This thing already seems to have a problem. The person testing it says that "the tone knob makes almost no variation in tone (doesn't get dark, regardless of cap) until about 1.5 at which point it gets dark and the volume drops off. If the volume is on 10, tone doesn't really do anything." So I turned yet again to the GuitarNutz forums. Where is the problem in this circuit.
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Post by newey on Oct 8, 2010 8:28:11 GMT -5
A tone pot, in order to work as such, must have a capacitor between one end (usually the CCW lug if wiring it for rt-handed use) and ground.
Putting a cap between the vol and tone pot results in the tone pot always "seeing" that cap- which would be expected to produce the results your friend reported.
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Raz59
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Post by Raz59 on Oct 8, 2010 8:43:14 GMT -5
A tone pot, in order to work as such, must have a capacitor between one end (usually the CCW lug if wiring it for rt-handed use) and ground. Putting a cap between the vol and tone pot results in the tone pot always "seeing" that cap- which would be expected to produce the results your friend reported. The capacitor to be tested would be between the alligator clips in the picture I supplied and the path for high frequencies would be pickup - capacitor - potentiometer - ground. It would a high pass filter facing variable resistance to ground. In theory, this would act like a normal tone control. But what my friend reported was not normal. Or was it?
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Post by ashcatlt on Oct 8, 2010 10:20:29 GMT -5
We've said it here a number of times before. Most of the action of the tone pot on a guitar comes from its loading of the high impedance, high inductance pickup coil and it's relationship with the capacitance of the cable. The cap itself doesn't actually come into play until the pot is almost all the way down.
The loop pedal is undoubtably buffered on its output, with a comparatively very low, mostly resistive, impedance and will not interact with the cable capacitance in the same way that a passive pickup would.
In short, your "test rig" is working about the way I would expect. Worse, it won't actually tell you anything about how that cap will sound in the guitar itself.
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Post by thetragichero on Oct 8, 2010 11:30:12 GMT -5
i need to get some alligator clips and get to work testing the various capacitors i have in my guitars i've been relatively lazy about it/occupied with other projects
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Post by sumgai on Oct 8, 2010 11:53:00 GMT -5
raz,
I see that you've got the tone control after the volume pot - not so good. Try moving the alligator clip over to the lug where the signal comes in from the looper, that should help.
HTH
sumgai
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Raz59
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Post by Raz59 on Oct 8, 2010 14:54:17 GMT -5
We've said it here a number of times before. Most of the action of the tone pot on a guitar comes from its loading of the high impedance, high inductance pickup coil and it's relationship with the capacitance of the cable. The cap itself doesn't actually come into play until the pot is almost all the way down. The loop pedal is undoubtably buffered on its output, with a comparatively very low, mostly resistive, impedance and will not interact with the cable capacitance in the same way that a passive pickup would. In short, your "test rig" is working about the way I would expect. Worse, it won't actually tell you anything about how that cap will sound in the guitar itself. That's what I feared...I went to the Boss pedals website to check, and input impedance differs from output impedance (output is much lower than input), I'd imagine that there would be a problem around it. Then how can I treat the buffered signal in order to simulate the output of a guitar pickup? Or is this too much wishful thinking and it's only possible with actual coils in the circuit? raz, I see that you've got the tone control after the volume pot - not so good. Try moving the alligator clip over to the lug where the signal comes in from the looper, that should help. HTH sumgai How much would it help, though? One other part of the test was to test and exemplify the audible effects of putting the cap before the volume pot (modern wiring) and after it (50's wiring)...
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Post by JohnH on Oct 8, 2010 16:02:10 GMT -5
The idea of using a loop pedal for testing things downstream is a good one in some cases, Ive done it myself. But it is entirely no good at all for testing the interaction of guitar tone controls and guitar pickups - since it eliminates the pickup, there is nothing to be learned by doing it. You could try feeding the loop output through another pickup in series, then to the test circuit, but it would probably still not represent just a natural pickup.
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Raz59
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Post by Raz59 on Oct 8, 2010 16:44:03 GMT -5
If it doesn't represent a pickup, then the idea is flawed from the get go unfortunately...if the problem was about the buffer and the resulting low impedance, then maybe bypassing the buffer module altogether would be a possible solution (I think).
Putting a pickup in series seems promising. If it were the same pickup used to generate the original signal, would tone control behave like the real thing?
Sound-wise, there might be differences, but as long as the response is consistent with the "real thing", then the test would be viable!
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Post by ashcatlt on Oct 8, 2010 18:07:03 GMT -5
Seems to me like it would be possible to run the looper in series with the pickup installed in the guitar. You'd record your loop, then disconnect the guitar and hook it to the test rig. If you want something semi-permanent, you'd need three jacks: From Guitar, From Looper, and To Amp. If these are in a conductive enclosure, the "From Guitar" jack will need to be isolated so that its sleeve does not conduct to that of the others. Tip from the Looper jack goes to sleeve on the Guitar jack. Sleeve of Looper jack goes to sleeve of Amp jack (you can use the enclosure for this) and tip of Guitar jack to tip of Amp jack. Should work. Might be noisy.
It's important to keep in mind, though, that the signal recorded into the looper will already have been affected by the pickup inductance and cable crapacitance, which will now be duplicated. Better might be to use a sine sweep or noise generator and view the output on a spectrum analyzer, but that's probably less than satisfactory again.
A sustainer driver coil would work to take the human element out, but it can be difficult to evaluate treble response without an actual attack.
Best would be an automatically picking machine. A small motor with plectrum attached. Keep it away from the pickup, though, as it will induce its.own tone via EM interference.
I think it's ultimately a waste of time. The external tone tester thing is not a bad idea, but taking the "human element" of a real person strumming the guitar out while leaving the subjectivity of listening for changes seems a little questionable. Also,
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Post by JohnH on Oct 8, 2010 18:25:22 GMT -5
Well, the idea has potential with the extra pickup, provided the looper was connected by a very short cable direct to the pup so there are no losses pre-loop.
You could try it, and judge first whether the sound with that rig is close to that of the basic guitar set up. If it was audibly enough the same, then it might be worthwhile. Even if it was just close, the ability to do very quick A/B swaps might reveal some insights into the effects of cap values etc.
Further, just thinking about the frequency response of this test set up, if one was to model this arrangement with 5Spice or similar, with pickup/signal source, buffer(loop), pickup (just acting passively), then pots and caps, I believe the results would indeed be very close to that of the basic normal set up.
So, better try it!
John
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Post by ashcatlt on Oct 8, 2010 18:43:42 GMT -5
^Except, again, for the fact that it would include the rolloff of the pickup inductance and cable capacitance twice, since the original loop will contain that signature.
I wanted to mention that I think the human element of the equation is in fact important, and should probably not be removed from the equation. A different tone just might make you play differently, and it is really that practical impact which is (in my mind) more important than any "objective" comparison of frequency response.
Another thing I wanted to say. I mentioned this earlier, but I'm going to reiterate. For most of the sweep of the tone pot, it is the cable crapacitance which is responsible for the low-pass action. You should not hear much difference between two caps until the pot is almost all the way down. We use pot size (250K, 500K, no-load, etc) to set our "10 tone" and the cap value to set our "0 tone". For that reason, if we're looking to test the difference between various caps, I feel the variable resistor is superfluous. I think it would be more useful to replace it with a rotary switch to replace your alligator clips for selecting different caps.
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Post by JohnH on Oct 8, 2010 19:19:44 GMT -5
^Except, again, for the fact that it would include the rolloff of the pickup inductance and cable capacitance twice, since the original loop will contain that signature. I believe, if the cable from pup to buffer is very short - then the cable capacitance effect is v small, and the inductance of the pup also has minimal effect since it has nothing to interact with- at least thats waht the math predicts. Then the extra dummy pup after the buffer will aproximate the desired interactions downstream J
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Raz59
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Post by Raz59 on Oct 8, 2010 19:42:00 GMT -5
^Except, again, for the fact that it would include the rolloff of the pickup inductance and cable capacitance twice, since the original loop will contain that signature. I wanted to mention that I think the human element of the equation is in fact important, and should probably not be removed from the equation. A different tone just might make you play differently, and it is really that practical impact which is (in my mind) more important than any "objective" comparison of frequency response. Another thing I wanted to say. I mentioned this earlier, but I'm going to reiterate. For most of the sweep of the tone pot, it is the cable crapacitance which is responsible for the low-pass action. You should not hear much difference between two caps until the pot is almost all the way down. We use pot size (250K, 500K, no-load, etc) to set our "10 tone" and the cap value to set our "0 tone". For that reason, if we're looking to test the difference between various caps, I feel the variable resistor is superfluous. I think it would be more useful to replace it with a rotary switch to replace your alligator clips for selecting different caps. The point of the capacitor test isn't hearing different valued capacitors or just the sound when it the capacitor is fully on (tone knob at zero or capacitor directly connected to ground). In two blogs (namely planet z and kernel of wisdom), two great hearing tests were done, and I've come to the conclusion that different capacitors of the same value (like Ceramic, paper-in-wax, paper-in-oil, mylar, poly film and mica) attenuate frequencies in similar, yet slightly different ways. I admit that it's kind of nitpick-ish The most striking example is, for example, comparing a ceramic disc capacitor to a mylar capacitor; compared to the mylar one, the ceramic cap seems to drastically attenuate medium-high frequencies, resulting in a harsh high end spike. These results can even be heard when tone knob is at 10. This testing rig was just taking a step further and improving these hearing tests. A consistent sound loop, free of the players inspired/varied pick attacks and such.... So back to the rig's problem - I connect a pickup directly to the guitar's output jack. Then I use a very short cable to link the guitar's jack to the loop pedal's input in order to reduce the cable capacitance's effect. After that I connect a pickup in series to the output of the pedal, and from there I connect it to the testing rig, like so: One question though: shouldn't I remove the pickup's magnet? Passing the pedal's signal through the coil generates a magnetic field by its own...won't the magnet interfere? Thanks to all participants in the thread, I appreciate the help immensely.
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Post by JohnH on Oct 8, 2010 20:07:54 GMT -5
I'd say keep the magnet, so the inductance is not affected. On the rig, the pedal ground goes direct to the vol and tone pot grounds and output ground, without in volving the pup. The dummy pup just has two connections, one to the pedal hot and one to the pots etc, so the signal runs in series from hot pedal output, through dummy pup to pots.
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Post by newey on Oct 8, 2010 20:22:58 GMT -5
JohnH suggested: I agree. If we're eliminating variables here, the one variable no one has mentioned is the looper- the extent to which it accurately reproduces the cap set up in question. There are sure to be some losses in that box; perfect sound reproduction is a goal, not a reality. Of course, you can say, "well, I'm going to A/B both signals through the looper, so that variable becomes a constant"- but it isn't, really. You'll never know if the looper might not be affecting certain frequencies that one or the other cap might not also be affecting at the same, so as to compound the effect in some areas and minimizing it in others. So JohnH's idea would at least give you a baseline to work from. If the signals are too different, it's probably an exercise in futility. If they're reasonably close, maybe it's a useful exercise. Remember, these are subtle differences you're exploring, so even a subtle difference in the output can color your results. But it is an interesting exploration, I hope you do get some results you can share with us.
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Post by sumgai on Oct 9, 2010 0:50:29 GMT -5
ash, Most of the action of the tone pot on a guitar comes from its loading of the high impedance, high inductance pickup coil and it's relationship with the capacitance of the cable. The cap itself doesn't actually come into play until the pot is almost all the way down. .... For most of the sweep of the tone pot, it is the cable crapacitance which is responsible for the low-pass action. You should not hear much difference between two caps until the pot is almost all the way down. Not true, not at all. Sagans of players have invested in ChrisK's RF Cables, myself included. Here's mine: Pretty short "cable", no? I can't recall ever hearing any complaints about unresponsive tone controls when going wireless. Indeed, they operate so exactly the same way as when using a premium cable (quality, not price), which is usually something a player remarks on (complains about), if there's a noticible difference between the two methods. ~!~!~!~ raz, Two things for ya..... Ask JohnH why we use "modern" wiring versus "ancient", he's done the tests. Short story, using vintage (ancient) is usually detrimental to tone. And, most looper pedals are meant to work at line levels, not guitar output levels. You might need to introduce some buffering to reinstate the average guitar level (and while you're at it, the average inductance, impedance and capacitance values). Not too hard, one should think. HTH sumgai
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Raz59
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Post by Raz59 on Oct 9, 2010 7:28:55 GMT -5
~!~!~!~ raz, Two things for ya..... Ask JohnH why we use "modern" wiring versus "ancient", he's done the tests. Short story, using vintage (ancient) is usually detrimental to tone. And, most looper pedals are meant to work at line levels, not guitar output levels. You might need to introduce some buffering to reinstate the average guitar level (and while you're at it, the average inductance, impedance and capacitance values). Not too hard, one should think. HTH sumgai Yes, I realize that modern (with treble bleeds) is the way to go...at least for me. Some people are still stubborn and claim that that ancient type of wiring "opens" up the sound, etc etc. Recently, someone mentioned that this might be the ideal treble bleed: It doesn't interfere with the volume pot's taper and if it gets overly bright at low volumes (common problem with treble bleeds), rolling down the tone reduces the effects of the treble bleed and engages the tone cap. I found it interesting but it's off-topic. If the pedal needs an external buffer, while it's probably not hard to build one, I can't possibly ask the guy testing it (by the way, the guy doing this is the writer from the blog kernelofwisdom I linked earlier). He's probably trying the version that JohnH suggested: If that doesn't work well, he'll probably do the test using an e-bow...much simpler than wiring a pedal into a buffer into a pickup into the testing rig into the PC... Again, thank you all for the thoughts.
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Post by ashcatlt on Oct 9, 2010 7:49:40 GMT -5
Raz - with your stated goal in mind, I'd want the most objective test possible. I'm thinking short bursts of white noise recorded to the computer and analyzed with waterfall plots or something similar.
It doesn't seem to me that emulating the action of the guitar is really all that important in this case, since the different caps should exhibit these properties independent of the source. A smaller pot would help make it work better with the low-Z pedal output.
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Raz59
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Post by Raz59 on Oct 9, 2010 9:43:59 GMT -5
Raz - with your stated goal in mind, I'd want the most objective test possible. I'm thinking short bursts of white noise recorded to the computer and analyzed with waterfall plots or something similar. It doesn't seem to me that emulating the action of the guitar is really all that important in this case, since the different caps should exhibit these properties independent of the source. A smaller pot would help make it work better with the low-Z pedal output. But ash, what are your thoughts on making the pedal's buffered signal pass through a pickup? Wouldn't this scenario provide similar conditions to what we want to simulate? The volume/tone pots would be loading a high impedance/inductance source (the signal would be coming from a coil), or is this wrong? As to the white noise test and waterfall plot analysis, I think that's waaay too academic! While it would certainly provide more objective data, the goal here is a simple hearing test to discern the attenuation of different caps on the same signal.
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Post by ashcatlt on Oct 9, 2010 11:26:56 GMT -5
Yeah, I think it's an interesting idea for a number of reasons, which is why I offered my suggestion on how to wire it up. Once you've got the test rig wired up, you could use about anything you wanted as a test source, as long as it had a low enough out-Z to avoid skewing the results too far. Seems I tried something similar a while back, but I was just messing around and didn't come up with anything particular interesting.
The reason I suggest white noise and waterfall plots or something similar is that you are looking for very subtle and (to my mind) questionable differences. Possibly more important: you're looking for differences. Human ears - and the brains to which they are attached - are fickle and sloppy and not very good at this kind of comparison testing. I personally will not trust your results unless they are conducted in a double blind manner with a number of subjects, at least some of whom are neither musicians nor audio professionals. And it'll have to be done in an acoustically controlled environment, maybe with isolation headphones. For example, what do you think would happen if the forced air heat kicked in as you were switching caps?
White noise and waterfall plots - or maybe a null test or something similar - would be easier and more convincing than all that.
Edit - I had written this whole thing on my iPhone, then the battery died just as I was going to hit the post button and forgot...
I'm a little worried about the ebow thing because I think the harmonics of relevance here occur mostly during the pick attack. If used (in?)correctly, the ebow can sometimes cause the strings to rattle or buzz on frets, or even on the ebow itself. That might produce some of the higher frequency harmonics we're looking for, but you'll have to try it, and it certainly is worth a try. You'll want it to stay in exactly the same spot throughout the testing process.
Don't let me dissuade you from your attempts. Take my comments not as dissent (though I can see where they come off that way) but more as constructive criticism or things to watch out for. We can learn a lot from experiments like this, even when they "fail". And anyway, it's a good way to waste a Saturday afternoon hanging out with a friend!
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Post by JohnH on Oct 9, 2010 14:39:36 GMT -5
Here is a 5 Spice model. The lower diagram represents a normal guitar, with a vintage PAF-style pickup and 500k pots and 22nF tone cap. The pickup inductance (3.8H), resistance (7k) and self capacitance (130pF) are modelled. To the left of the circuit, a 1M resistor and 0.5nF cap represent input impedance to an amp, through about a 10’ cable. The upper diagram inserts a neutral buffer, within the blue box, representing a loop pedal, with fairly common values of input and output impedances of 1M and 2k, after which another passive pickup is in series before the pots etc. Here are the frequency response graphs, at minimum and maximum tone control settings: The output for the basic guitar is the dashed blue trace, while that through the buffered rig is red. The curves are reasonably similar, with an extra blip in the high treble of the test rig, due to the self capacitance. So it looks close enough to be worth trying, but it may not sound exactly the same. Cheers John
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Raz59
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Post by Raz59 on Oct 9, 2010 21:37:17 GMT -5
Fantastic! Despite the worrying dip at the 7.5kHz range, at least the mathematical models of both situations look the same. And since the graph is about frequency response, they also respond in an equal manner, which is exactly what is needed! Thank you very much JohnH, the testing rig will work as intended. ashcalt, I do understand the shortcomings of the mind, your worry about false-positives induced by it and importance of making these kind of tests in a double blind fashion. I'm extremely skeptical when I read about how a change of capacitors in a Les Paul (from a mylar cap to a Sprague Bumbleblee paper-in-oil cap) is a "huge"change or that it was "really" noticeable, etc. I take those kinds of statements with a grain of salt. I know of only two tests that are blind tests, and they're from the blogs I've linked. The direct links to the blind tests are here and here in case anyone feels like wasting 10 minutes. With a good pair of headphones, maybe you'll spot the little differences I referred to earlier. I'll eventually bump this thread with yet another cap test, and it'll include "audiophile" grade caps, vintage ceramic caps and an assortment of other oddities. Thanks again!
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Post by sumgai on Oct 10, 2010 2:07:38 GMT -5
raz, I had thought mentioning the EBow, but I'm with ash - the initial pick attack sound is a goodly portion of what we hear, and define, as "tone". The EBow, on the other hand, is indeed meant to influence the tonality of the string/pickup combo. In fact, there's even a switch meant for just that purpose - "Harmonics", I believe it's called. I think John's got you covered pretty well. If you're building a rig anyways, you might as well include the necessary components that will emulate as closely as possible the output of the guitar. The looper itself will handle the transients of the pick attack, and pass them on pretty faithfully to your test jig, so you might as well try to handle all of that signal, if you possibly can. BTW, it's a well known fact around the NutzHouse that I hold in total disdain any sound files reproduced from a website, and subsequently played on a computer. From the source to the final audition in one's headphones, there are way too many uncontrollable variables to ensure that all listeners hear the same thing in the same way. IMHO, of course. HTH sumgai
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Raz59
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Post by Raz59 on Oct 16, 2010 9:40:48 GMT -5
Update on the rig. My friend wasn't able to get it to work, unfortunately. He did the test in a similar fashion like the last one. The test can be found here, and is available in a blind test format. He used his fingers, to pluck and strum, so some tonalities can be explained by that. Again, thanks to all the resident Nutzies for the help, I'm off to my next guitar project...
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Post by cynical1 on Oct 16, 2010 13:49:45 GMT -5
While I agree with most of sg's point about website sound files not falling under the scientific model, if all factors are generally equal it can provide a good indicator. That being said, I was surprised at the Russian caps. I can see a market here in the US for those... Granted, I tend to cast a cynical glare at most things, but just the novelty alone...coupled with the marketing hype of "retrieved from the old Soviet space program" or "pulled from decommissioned ICBM's" could make the right marketing weasel a nice little chunk of coin... As ChrisK would have said...Marketing Is! Happy Trails Cynical One
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Post by JohnH on Oct 16, 2010 15:10:42 GMT -5
Well, whether or not one believes in capacitor tweaking, I think that was as well set up a test as could be done over the internet, nicely recorded and well presented, so I gave it a careful listen using good headphones.
I did the blind test, and clicked on each to listen to all the first 'tone at max' settings first. I couldnt pick any differences, but then maybe I'm biased because the theory tells me I shouldnt be able to, or maybe the theory is correct!
Then I listened to the end of each sample, with tone at min. I'm proud to say that I correctly picked out the brown 0.1 cap, and also the no cap! (I'm not sure how that one gives a sound at all if the knob is at minimum)
The others I did not pick out first time, but once I got the answers, I listened again to the Vitamin Q (0.017) and Ceramic (0.026), and could hear a difference - I think the smaller value would be more useful. I couldnt pick anything significant between all the ones nominally close to 0.022 however, but again I am biased.
The mid settings also all sounded similar to me.
Anyway, I think its well worth a try.
John
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