Use Saw Studio as a Way to Determine Resonance in a Guitar Pickup

[Dave Labrecque]

Dave,

"Can you dig it?" ... simply, "Nope!"

I would just like to know "Why?" It is because it is there... or just bored! I am NOT meaning to be rude or obnoxious - I am simply curious to know why...that is all!

I can't speak for John, but many people like to try new things. New approaches. In their art.

I figure if Paul Reed Smith has a reason, it's likely valid.

Have you seen the PRS video? I think he explains his thinking.

https://www.youtube.com/watch?v=OUcPdtJ3dO0

Listen to what he says starting at 2:07.

[mr_es335]

Dave,

I did that...as well as from many "other" developers.

All but one, provided me with an answer to my question "Why?"

As a point of interest - and I know that we have gone rather south here, i the old days of using a Strat, you had three positions. The someone discovered that you could position the switch in-tween two positions - arriving at another timbrel output. So, later Fender came up with a five position switch! This, I get!

When it comes to what John - and indeed, others are doing, two terms come to mind, 1) audience and 2) diversification. A proper understanding of these two terms - in particular, as these terms pertain to musical performance.

[jmh]

>Why?

It is the perpetual quest of tone!

Personally I'm not a guitar player who can dial in specific tones. However I sometimes enjoy wandering around in search of sound - it is another dimension to the fun of guitar playing. When you dial into a great sound it is fantastic. When you learn an interesting riff it is fantastic. New and better technique, great too. Discover an interesting scale to play around with that lets you venture into a new direction - fantastic. Still all of that is kind of trivial compared to doing it for and/or with other people.

Nobody who is listening gives a **** how you hold a guitar pick. I've seen guitar players that have amazing technique that don't move me at all. On the flip side, there are some unaccomplished musicians or rudimentary songs can really move me emotionally - sometimes every time I hear them - even over years. I know which of these categories of music I prefer to listen to. Of course the best players are those who deliver both of those dimensions - still a ton of the great players violate many norms of what is considered the 'proper' way to hold, pick, fret...

Playing with sound is something that can make you more present in the music and help you keep your ears open. If you devise a gadget that makes you sound a bit unique - particularly on a world that has millions of guitar players, is something you can be proud of. It's just like effective use of tone control or a 5 position switch - but even better because its yours. If it makes you happy or is just fun, that is great because these are all fantastic emotions to incorporate into and enrich one's music.

If you think your notion of how to play is the best or only way to play, you are probably not very interesting to listen to, and almost certainly would improve your musicality by opening your mind...

[Cary B. Cornett]

Cary, I like your flux loop idea, although I worry about introducing noise into the system. At the moment, though, I don't see any other alternative. So, unless something better pops up - I'll probably try it.

You mean using the flux loop to inject pink noise, right? And yes, there are other test signals.

It has occurred to me that my original stipulation of exciting the circuit using pink is unnecessary. My reasoning is that pickup resonance isn't harmonically produced, so there's no reason to muddle up the screen with other frequencies. Rather, it's more 'mechanical', in that any electrical signal will be sufficient to cause it to be produced. So, in fact, a better solution would be to use a relatively low frequency sine. Then, when looking at the result on a frequency analyzer, there should be the known low frequency, plus a higher one that is generated by the LC sub-circuit. Any other lesser peaks I would look at suspiciously as probable noise.

Not all possible test signals will cause the resonances in a system to "pop out" where you can see them. If I wanted to test for that with a guitar on my test bench, I might go for the old fashioned method of driving a flux loop with my sine wave generator, and connecting the guitar output to my AC voltmeter. Once I had the level set so I could read the signal on the meter, I would sweep the frequency (the level from the generator stays constant) and watch for changes in level. As I got to the resonance frequency, the level on the meter would go up, and as I tuned past resonance, the meter level would drop again. The frequency at which the resonance occurs will be the one that gives the highest peak reading on the meter.

My guess is that you don't have those test instruments. This is where computer based testing software comes in. There are various applications available for this. Room EQ Wizard just happens to be the one I sometimes use, and it is free.

I haven't picked it up yet, but I'm curious what it is about 'Room EQ Wizard' that I'll like better than SAW for this application?

SAW is designed for recording and mixing. One can put a signal generator plugin into it, and can set up metering to read the return level to another input, but that is not what SAW is designed for. REW, on the other hand, is specifically designed for testing, and has various functions and features that do not exist in SAW. One thing you can do with it is program it to do a frequency sweep, and have it produce a chart of what comes back from what you are testing. The chart will show you exactly where any peaks are. This is faster and easier than the method I described above.

The swept sine method is probably the best way to find where any resonance is. And if you wanted to tinker with "tuning" your pickup resonance with component changes,, repeat testing is much faster when you can automate it. What I don't know is the extent to which magnetic couple with the guitar strings may affect pickup resonance.

[jmh]

I also wanted to mention (for the non guitarists) that guitars themselves each have their own resonant frequencies. These can be from wolf tones of the string trees, truss rods, loose parts, a particular piece of wood (neck, rib, top...), various cavities, and of course in the case of hollow bodies and acoustics the resonances within the body. Any one of these things is at the ready to sing with the fundamentals or harmonics of a played or un-played string. Also the back portion of a fretted string (although it is undeniable that nice fretting and muting techniques can control this somewhat).

Certain guitars like certain keys better than others - and you may gravitate to play certain chords sound better - particularly when you have irregular fretboard wear, intonation adjustments that favor certain keys or 'your' particular playing style. Also many players will tune the strings a bit different than an electronic tuner would suggest.

A first guitar during your formative years can really ingrain its character on your playing - and you can be totally unaware of that relationship, and its impacts when you interact with different instruments later on.

I have a Taylor 810 that had the case lid fall and the buckle cracked the top. It has must have softer frets than other guitars I have that have worn less with more play, so the intonation is now less precise than it once was. Still I'm reluctant to get it repaired because it sounds fantastic. This guitar 'wants' to play certain things, and I have to switch to a different guitar when I want to do other things. It is not because it can't be played on either, it is because it is a more rewarding experience on one over another. It is also refreshing to the ear to have a different sound to get acquainted with, or an old friend to get re-acquainted with.

I think having a knob that can adjust one of the variables in this bewildering equation to enable one to tune tone (which is different than rolling off a portion as conventional tone control does) is a super cool idea.

On an aside, one of the things I love is the sound of guitar shopping in a room full of acoustic instruments. It can be totally misleading when there are dozens of guitars, ukes, and mandolins singing along with whatever you are playing - it's always wise to move around, step into a different space. I guess the really successful stores have good rooms to get you that way too...

[Dave Labrecque]

Dave,

I did that...as well as from many "other" developers.

All but one, provided me with an answer to my question "Why?"

As a point of interest - and I know that we have gone rather south here, i the old days of using a Strat, you had three positions. The someone discovered that you could position the switch in-tween two positions - arriving at another timbrel output. So, later Fender came up with a five position switch! This, I get!

When it comes to what John - and indeed, others are doing, two terms come to mind, 1) audience and 2) diversification. A proper understanding of these two term - in particular, as these term pertain to musical performance.

Not sure where you're going there, Dell. But consider these two ideas:

1) How is John's quest for more total variations any less valid than adding additional pickups to a guitar? Or adding additional positions to a guitar's pickup switch?

2) Think of John's visualization of a knob that controls a spectrum of resonance states as analogous to deciding you want more positions on your pickup switch than five.

We obviously all have our individual preferences when it comes to how we'd like to experiment with guitar sounds. Why deny John his?

[John Ludlow]

I've continued to research capacitors and their use within electric guitars and it has brought up something troubling for me. For those who, like me, did not know, the tone control on a guitar is actually just a pot, like the volume pot, except, it has a capacitor on its exit lug that actually leads to ground. Without it being there, whenever that pot is turned up (less or no resistive material in the circuit) all the sound produced by the guitar would go to ground rather than elsewhere where it can be heard. But the capacitor prevents that. It only allows frequencies above whatever limit its capacitance allows to pass through. So - those high frequencies get sent to ground and are never heard from again - and the frequencies that it does not filter are what we hear. The amount of capacitance represented by that capacitor controls how much of the high frequency the tone pot has the capability to send to ground. And the amount of resistance from the pot controls how much of the signal becomes available for the capacitor to filter.


So, none of that is troubling in itself. It's kind of genius, you know? The simplicity and efficiency of it? I'm now wondering where the capacitance that combines with the inductor coil to produce a resonance pitch is located? Is there something implicit in the construction of a guitar pickup that creates capacitance? Or - is it using that same tone capacitor to do it?


And here is where the troubling things begin for me. A capacitor, in a sound circuit, filters out all the frequencies above a certain pitch inherent to its level of capacitance. So, if the pitch of the pickup resonance I'm trying to have control over is within that range - doesn't it get sent to ground too? It, at least, certainly seems like it would, most especially if it's using the tone capacitor for that half of the cap/inductor sub-circuit.


But, maybe there is some inherent capacitance built into the materials of the pickup itself? All this time I have understood that there will be a single tone that is produced by the 'oscillation' of the capacitor and inductor. If it's 'built-in', why isn't that inherent capacitance wiping out all the frequencies below its filter activation point? Why are there not only high frequencies left?


These questions are going to require an LCR meter. I've picked one out on Amazon - but I haven't ordered it yet. I don't see any way around it though - I'll have to get one.


But it also adds troubling issues for the idea of adding capacitors to the circuit in order to multi-vibrate with the coil to result in resonance at multiple different frequencies, because - they would be filters and one of them would wipe out any effect of all the others.


So - I'll test it when the meter gets here. But presuming that my idea is simply unworkable, I have a separate idea that has come up for me in the meantime that might also be cool (albeit less so...).


Instead of using the one tone capacitor to control how big a bite of the frequency range the tone pot sends to ground, how about wiring in a variable capacitor to do it instead? Most Strats use either a .1 or a .022 picofarad, non-variable, cap with the .1 taking a bigger frequency bite and resulting in a 'warmer' sound, and the .022 taking less of a bite and resulting in a higher-pitched sound. Maybe one could cover all of that range and more, allowing one to have the advantages of each - and more? From a wiring perspective, you'd just unsolder the existing tone capacitor and wire leads to the new variable cap to those same locations.


I note that there are existing, after-market, products that employ a multi-position switch with a different, non-variable, capacitor at each stop to accomplish exactly this already. Why not one that is infinitely variable between two extremes instead? One possibility is shielding. Popular tone capacitors have one thing in common - they're physically sort of a tube with a wire in the middle of it that doesn't touch the tube, and some non-conductive material between them. When wired correctly, the tube part is the portion that ultimately leads to ground. This configuration inadvertently results in the portion that doesn't go to ground being shielded from electromagnetic fields - a very nice thing for single coil pickups, which are inherently noisy - if you have never played one.


Whereas, the variable capacitance pickups I have looked at look more like multi-layer pots, but with a dielectric material separating layers of conductive ones. These would not be inherently shielded. But... maybe you could shield them yourself somehow?

[John Ludlow]

Cary - I will look into the software you recommend. But there is one detail that I disagree with you about. It has to do with the whole concept of pickup 'resonance', actually, and how it differs from other kinds of resonance. If a room is resonant, for instance, you will only hear its resonant frequency if a sound with that pitch (or one harmonically related to it) causes the room to vibrate.

Whereas pickup resonance, if it exists at all (see above...) happens differently. The capacitor/inductor relationship causes a sine wave to be produced of a frequency that is controlled by their capacitance/inductance values. The capacitor builds up charge until it ultimately overwhelms the dielectric material and a pulse of electrons breaks through and is sent to the pickup coil (the inductor) which causes the coil to store the charge as a magnetic field. But then the capacitor has no charge - and the inductor turns some of its magnetism back into electricity and feeds it back to the capacitor - re-charging its electric field. This swap of the pulse back and forth between the two components happens at a specific rate that is independent from the frequency of the guitar playing that is exciting the circuit. So, it's always being produced at that same pitch regardless of the frequency of the signal. That is - up till this point - there is no resonance - there's just a sine wave added on to the signal that wasn't originally there. Essentially, it's very consistent distortion produced by the circuit.

The resonance happens when a frequency within the signal happens to be the same as the frequency of the sine wave produced by the cap/inductor. The combination of the two sines together is louder than either one individually - and only at that one note (or one harmonically related to it). Calling it 'resonance' is probably correct, but it's misleading too because it is so different from, again say, room resonance - where there is no noise from the room until the signal at that resonant pitch triggers it.

As a result, I was thinking that one could isolate that 'distortion' pitch by providing the energy needed to produce it as a non-harmonic signal frequency that is much lower than that 'ringing' produced by the cap/inductor. Then there should be two frequencies in the resulting signal: the original input low note, and the cap/inductor ringing/distortion. At that point it wouldn't be resonance at all. But it should still show up on a frequency analyzer - and it would be very clear which was produced by the cap/inductor - because there would only be two pitches on the screen.

Does that make sense? Do you agree?

[John Ludlow]

Dell, at the risk of pulling your finger, I'll answer your question. But it's going to require some background. And you're likely to think it's a little weird.


For me, music is an emotional language. There are things that cannot be transmitted between people in text or concept. These are fleeting experiences that we all have, moment by moment, as we travel through life and react to its variance, that are much more subtle than 'happy', 'sad', 'angry', etc. When we talk to each other, we relate some of these as subtext in the way that we deliver our message. They are experiences that are too nuanced to have names - but are known to us just the same.


I used to have a good voice. Back when I was able to sing, I would use those signals to enhance the subtext, in the song I was singing, evoking those subtle and fleeting emotions that the listener could relate to and understand. Tiny variations in delivery that carry more meaning than the words can, emotionally. And it was all unconscious. When I was dialed in, I could relate the precise timbre of pain or joy or confusion that each note in the song expressed to me in a way that would resonate within the listener. They're things that are much too complicated for me to have intellectually engineered.


When I play the guitar, the words (the concepts) themselves aren't there. That leaves only the train of subtle emotional experiences to relate. And, as with singing, I am incapable of engineering them. Instead I rely upon some other part of me to somehow instill meaning within the string that I pluck. And that part of me, if it even is part of me, happens below, or anyway, somewhere other than, my conscious reality. I question its locale because again, when I'm really dialed in, I stop being aware of being the player at all. The experience is as if something reaches through me to access the strings. I'm only a witness to it happening - I don't actually do it myself.


And that experience is as if a higher power is playing me. As if it is using my proficiency and the variety of sound available to me in my instrument as a pallet to evoke those subtle emotional experiences - and I'm just watching/feeling it do it. It feels like emotional bliss and freedom to me to sort of become the instrument in between this higher power and the guitar. And I'm addicted to it. I'm a junkie for it. Or maybe I'm its lover. It's the reason I still play after all this time, when so many other things that were important in my life when I was 12 have been cast aside and forgotten: to have direct personal access to that connection again tonight.


But there are degrees of access to it. And sometimes I just can't get there at all (and I really hate that...). Often, in those circumstances, the problem seems to be that the sound is just... 'wrong' somehow. Inadequate to the task. I mean, it's the same guitar it was yesterday, and the controls haven't moved, and yesterday it was sufficient. But, the muse is fickle. It won't tell me what it wants - only that this isn't it. And I cast around trying to make an adjustment to make it 'right' again - to please her. I have all kinds of equipment I can use to change the sound. I'll adjust the tone control on the guitar, or those on the preamp, or the equalizer. I'll add or subtract delay - or turn it off or on altogether. Whatever it might want - I try to provide. Would you care for some Red Silk tonight, my love? No? Yes, of course not - what was I thinking? Perhaps some of the Blue then? You liked that on Thursday, remember? And she gives me no hint what she demands - only displeasure or satisfaction. And I'll try anything to please her. I'm a fool for her love.


And so having yet another way to modify my tone - in this case the resonant frequency of the pickups, is attractive to me. Maybe that's what she wants tonight? Or - maybe not. But... maybe so?

[Dave Labrecque]

it is so different from, again say, room resonance - where there is no noise from the room until the signal at that resonant pitch triggers it.

Sorry to jump in here, but I think they ARE more or less the same kind of thing. As in the room example, the circuit needs some "activation energy"--at the correct frequency--for the resonant sine wave to emerge. I don't think any frequency of simple sine wave will reveal the resonance (theoretically). I think it would need to be some kind of broadband signal who's spectral content would coincide with the circuit's resonant frequencies in only one or a few points. OR, if not a broad-band signal, the exactly correct (or near-enough) individual frequencies would need to be inputted. Much like room modes in acoustics.

I could be wrong.