# Sustainer Harmonics

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Well., as has been mentioned..everyone has different goals for their sustainer. My thing is

I love the blooming harmonics created by a sustainer.

And my goal is to achieve lots and lots blooming notes... with some degree of control.

There are some things that I think I have learned from this forum... ( I could certainly be wrong ---

please feel free to correct me!)

I think that "harmonic mode" works by shifting the phase of the signal to the driver by 180 degrees from the

frequency put out by the pickup..... which acts to cancels out the main string vibration and allows a less

dominant frequency to take over and be sustained..........creating the "harmonic" bloom.

Right so far?

Also besides reversing the leads to the driver, modifications to the amp circuit are capable of causing some degree of phase shifting.. For example Pete's current circuit that causes his lower strings bloom.

And one of Col's posted circuits that has selectable (rotary switch) built-in filters specifically for this purpose.

I am wondering if this theory is correct.... Phase shifting is nothing more than very small delay between the input frequency (pickup) and the output frequency (driver signal)

For example for the frequency 440 hz ( open A) the string is vibrating 440 times a sec. If a delay was put on the signal of equal to half the frequency (220hz) then the phase would be shifted 180 degrees. this works out to be a delay of 1/220 = .0045 sec or 45ms. (if my math is correct!)

And a given delay would have more or less phase shift on the different frequencies.

The point is that a circuit that could create adjustable delay with a pot could have infinitely variable phase shifting,. and the ability to dial in all the harmonics available to a guitar.

So, the question is has anyone tried tiny delays on the driver signal?

Are such small delays even possible?

I was looking at this chip. PT2399

It has delays as low as 31ms...adjustable upward by changing the value of R. (put the pot here)

These are longer delays than desired, but wouldn't a longer delay (within reason) serve the same purpose....phase shifting?

I know people have mentioned trying delay pedals on the driver signal. and got weird effects but that is a much larger delay.

Anyway, I'm not able to work on my sustainer project at the moment. But cant stop me from theorizing!

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Well. RE. the above post... I think that I have a flaw in my theory.:

It actually helps to write these idea out. So thanks for indulging me.

A note will only bloom when it is hit with a 180 degree phase shift, Right?

That is necessary to cancel out the fundamental and allow a harmonic to take over

My variable phase shift would only vary which frequency was getting 180 degrees... all the others

would have a different shift. and not bloom at all. Not exactly what I was looking for

I was hoping to get adjustable harmonics on the same note.

Well not to loose all hope.. What if you pumped in Harmonics from a pedal like this

into the sustainer in order to overpower the fundamental?

I know.. probably not worth the effort, but what do you think of the theory?

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Phase shifting was something I worried about very early on and a lot of emphasis is put into the patents concerning this aspect. The use of filters to select for tiny delays is commonly used, the floyd rose sustainer patent has some easier to understand ideas on how they auto-selected filters with frequency.

I don't think such a delay chip is the way to go, we are looking at very tiny delays given the speeds a which strings vibrate...capacitors provide a far more effective way to go I might suggest, but these concerns seem to be the things that some are concerned about with the idea of digital processing.

My perspective was to create a driver design that was "fast enough" to work on the range of the guitar to avoid these phase concerns, rather than having a driver that needs compensation to get a good response over the range of the guitar. I believe that various simple designs have achieved that. It would seem that the driver designs of commercial units and some other proposals require such compensation circuits.

One problem is that the the drivers inductance will change with frequency and the guitar is not a monophonic instrument. So, if you play a chord, how will such compensation circuits handle such a signal? Perhaps the answer is hex designs, six amps and compensating circuits, etc...but really, this level of complexity...what is the pay off when a simple solution will work?

So, one way to consider the reversing of the driver leads. One might on the surface think that by reversing the process of string driving you would create an anti sustainer...and it is possible in special circumstances to observe such an effect. However, I look at it as stopping the main fundamental frequency and so leaving the next strongest harmonic in the series (very often the fifth above) to be driven...creating the harmonic effect. A bit like stopping the string at a modal point, leaving behind the harmonic behind it.

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The desire for "harmonic blooming" can easily be created as well as several novel harmonic effects with the conventional sustainer and the reversing of the driver leads. Having too much control that is hit and miss in performance would seem to be asking for problems...it needs to have some automation I'd suggest to be useful.

It needs to be understood that while the harmonics are predictable, they are not usually octaves. So, in playing, the note that sounds or blooms out of the initial note will not be the same pitch. However, it tends to sound musical since it is a part of the original notes harmonics. There is also the fact that in western music we use a tempered scale...the harmonic note created will be from the natural harmonic series. So, there can be some thinking about the notes fretted and the notes produced when playing or composing for the thing.

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My circuits are typically tuned to create an effect I like that is essentially a "compromise" in many ways. I like that organic bloom thing, especially in the lower range and am happy for these bass notes to evolve into others and keep things simple and responsive all over the guitar. I know Col for instance was very concerned that in the fundamental mode that low notes should ring as sounded. Adding more switches to alter caps could easilly achieve this, having a complex circuitry of frequency analysis that switches in delaying caps is a way that FR describes. Others may take in digital means. However, everything in the chain, especially things like digital processing, causes delays and phase shifts....even the driver itself...so, how much compensation are you going to do, who has the knowledge and equipment to truly calculate this out in the real world? What is the pay off for such complexities compared to simple solutions?

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There are things to explore and there may well be many things that surprise me, but given that the expertise in circuit design has failed to even address the standard circuit issue, even as they complain about the F/R solution offered up, or the mods to my specs suggested...seems to indicate that we are not there yet.

My experiments with things like flangers and delays in the early days were to explore these areas and i didn't find them that great. I have an old tycobrahe pedal flanger that can do static auto and pedal sweeps for instance...I got bird like chirps as the pitch shifting struck off various natural harmonics...I imagine this kind of thing would be the effect and not entirely useful.

My suggestion to anyone wishing to explore these things is to make a simple known working design to a standard that works and see if that fits the bill, or where it needs improving for your musical preferences. To me, time and again people seem to be reaching for solutions to problems that don't seem to be there, or going straight into complexities beyond their abilities (and mine) in anticipation of solving problems not there, or for marginal or unspecified gains.

There are limits to this stuff as well...it might be nice to imagine holding a chord and all the notes to come out evenly as an octave above...but I suspect such things are close to pipe dreams and similar or more controllable effects can be had with digital modeling with current technology on any guitar. You might thing adding more controls that are performance sensitive is a good idea...but you may need another player to operate these controls while you attempt to actually make music...no?

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So delays...I'd be looking at caps...even with a drastic change from say 220uF to 100uF on the output cap only effects harmonics on the very low end of the guitar. On bass guitars, I tried running caps at 470UF and higher and still getting harmonics. I don't think it is a predictable as you might imagine or as global to effect all the strings...the instrument could become so sensitive to such adjustments as to loose the predictability that is necessary, though it could produce a range of "effects".

Anyway...just a few thoughts...but you may well be surprised about how well simple approaches can work, and how adding any complexity can grow exponentially, and easily to the point of not working effectively at all. It's a very fine balancing act as I and many other have found out.

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First, magnetic drivers are local. Any harmonic has knots on the string. The fundamental one has knots at the bridge and the fret. The second - one extra knot exactly in the middle, the 3rd - two extra knots and so on. When you place the driver at the knot of the harmonic you can never sustain this very harmonic. And the positions of the knots depend on your left hand, so, you will inevitably have certain harmonics at certain positions that are impossible to sustain. Maybe there are some drivers on the bridge (piezo?), at least it's theoretically possible. I know sustaniac use piezo driver, passing vibrations through the neck. Similarly, you can theoretically design saddles with piezo drivers. It will solve the problem of knots.

Second, phase shifting is not just a delay. Ideally, there must be frequency independent phase shift, so that, at any frequency you would have a stable 90 degree (for example) phase shift. It can only be achieved with pitch detection and digital processing. Well, you can easily have 180 degree phase shift by just inverting the signal, but not arbitrary shift.

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I assume by "knots" you mean the nodes and anti nodes of the string. The theory that "you will inevitably have certain harmonics at certain positions that are impossible to sustain" does not mean there are dead spots...simply that different harmonics are sustained or driven. You won't get all 2nd order harmonics but this will change in a somewhat predictable nature across the board.

In practice, most drivers are big enough to span the 'point" at which vibrations cross and can drive the strings appropriately regardless. If you consider a guitars pickup, these do not prohibit harmonics being heard or dead spots because they are far bigger than these so called "knots".

Not sure the extent of "digital processing" that are a must, but the patents and current devices use various ways of effecting phase compensation for their drivers...FR is perhaps the easiest to understand from memory and an old patent now.

However, the kind of drivers and designs typically work very well without any phase shifting as they were intended to do. In my work, it was the late Lovecraft (bill love) on this forum that encouraged me to concentrate efforts on the driver to avoid the necessity of phase compensation. I don't believe any of the DIY sustainers (except perhaps dizzy's from another forum) have used phase compensation.

I did quite a bit of work on so called "acoustic sustainers" like the sustainiac model C and many variations. The transducer is magnetic and sits on the neck and requires a fair amount of power to shake the guitar neck. It too can suffer from different resonances in the instrument and the system. Piezo ideas have thus far failed on my side and seem very unlikely to work.

Also, driving on a node is perhaps not the best idea...this is kind of a fundamental still point...two certain nodes are the bridge and the nut. It would also appear to be some EMI like noise that can get through piezo systems with these types of devices, I am not entirely sure what is going on there. There are also a lot of lagging phase problems with anything mechanical...say my experiments shaking a strats fulcrum trem...there are significant momentum forces to overcome with such mechanical systems. Plus, they tend to make a racket and are not as efficient as applying the forces directly to the strings themselves.

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A few interesting harmonic effects that any sustainer can do and is kind of unique

If in a strong normal mode and you ping a harmonic (say 12 frets above the fretted note) it will morph back to the lower fundamental with the drive...so a reverse harmonic of sorts.

If the intensity is adjusted way down, below infinite sustain, as a note fades out naturally, the tail end will sound as a harmonic as it fades...great for adding a unique if subtle detail.

If you play a note, switch to harmonic mode while sustaining, it will rise to a harmonic, if you switch back to harmonic mode, often you will get still another higher harmonic, eventually it will return to the fundamental...a bit like a sustainer version of pinch picking harmonics along the length of a string.

A chord can have added harmonic extensions from harmonic drive on the predominate lower strings...a harmonic on my guitar on the lower strings tends to sound higher than the notes on the high e in the same chord.

There are some really weird "psycho-acoustic" kinds of effects you can get. I was playing with some of these last night...using a delay on the guitar and a tremolo arm, you can generate the appearance of two harmonics both rising and falling while 'pitch bending' in this way...tricky thing to do, but very cool.

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An effect of the driving of a string with a sustainer allows for the shaping of the envelope. It is possible to pick lightly or just fret an not and it be driven "from nothing", increase in drive and so volume, then can be cut short with muting...the result there can simulate in that instance a 'backwards guitar".

There are lots of other effects possible with these devices, the "problems" often exist in the ability of the player to treat it almost as another instrument, damping is incredibly important...it is possible with careful damping to lower the envelope then allow it to return for instance.

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I'm sorry to sound negative about the digital stuff, but we have heard these ambitions before and have led to nothing, at least so far. Same with many of these 'issues'. FF uses a compressor on the signal to effect an AGC, but that's pretty much the standard way of producing AGC.

The certainly is a lot that can be done with digital stuff with this project, but it would need to be tuned very carefully and probably specifically for any system and guitar. The processing itself takes time and any digital processing must have to compensate for it's own lag in responding compared to the direct analogue approach. It could work, but it will be tricky and the benefits are a little obscure to me in a comparative approach. The only way to really convince people of these ideas is to put them in practice. However, last time, over a year it morphed from a hex system to a mono/digital thing (using pics) to a basic amp and design very typical of what has been working for years...without any acknowledgment or disclosure.

So...I am wary of the "theoretical" discussions where the practical work is not done. Also, still not absolutely sure that I appreciate what is being searched for that a conventional simple sustainer can do. I can see where Col is going to a large extent and am confident that something will come of it.

Still...I'd love to be proved corrected. So far, in all the years and people coming and going, it has remarkably come back to very similar simple ideas that have persisted. In my own work at least...and I have tried everything from hex designs to piezos to "acoustic" versions, mid drivers, bridge drivers, mini ebows...the more conventional designs seem to have come out consistently more effective on many levels.

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Oh...I just saw your last post Al...

Pitch shifting was something I was considering...but not sure that this is worht the effort...it can easily produce and with more control to use things like the whammy pedal on the guitar itself...a different kind of effect, but certainly works.

Not entirely sure, but I think you would get that "reverse harmonic" effect...hard to tell without trying...but a lot of electronics and power hungry to put inside a guitar don't you think?

Another thing to consider is an auto-volume pedal like a boss "slow gear" to bring the drive in later in the form of the note...this would produce a "blooming" effect.

I'm not entirely sure though...it is this morphing to a harmonic that you are interested in? This will occur naturally if you lower the drive intensity a bit so that it takes a little more time for the sustainer to work it's 'magic' on the picked note. You can also use the drive control much as you would a volume swell to bring in the sustain and the harmonic effect which can be cool. It's still a lot to be thinking of while trying to play the darn thing though.

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I may have mentioned it before, and before I hit the road for a while...I ahve been considering making a taping instrument that is driven by a sustainer or even hex (or however many strings required) system. The idea is to damp it at the nut end like a 'stick' and use the sustainer to generate notes and swells just by tapping notes with both hands upon the strings. It sounds like a really cool potential for the technology...but potentially very difficult to play I imagine! I kind of envisage it like a lap steel or even pedal steel kind of thing, so potentially you could use your feet for controls and have less reservations about it being remote powered or overly compact in circuitry. Just a bit of imagining...

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i bow to the great psw for he is the sustainer god..

seriously having read most of the whole thread i am more than a little impressed. i am only sad i contributed so little but alas my internet and funding wouldnt allow as such.

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Yes, that's right, I namely meant nodes of the standing waves. I just read this term somewhere and it was obviously not quite correct. Thank you for the correretion.

A magnetic sustainer powered by the signal from the pickup, tends to amplify a single harmonic, eventually turning the sound into just a pure sine wave. Even if the driver is not exactly at the node, but close, the corresponding harmonic won't sound, simply because another one, that is close to its antinode will win. I noticed that it's a matter of competition. You have resonances at different frequencies with very high Q-factor, and the system with natural positive feedback loop. It means that one harmonic, that has the best resonance conditions wins. And it's not necessarily the fundamental one.

BTW, if you want to enforce higher harmonics, I'd suggest to try... a diode bridge at the output. I know, audiophiles would kill me :-), but it's just an experiment. Yes, 9 volts may be not enough because of significant extra voltage drop in the diodes.

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Hi Ansil...I know what you mean...but I still recall some interesting discussions early on about some stompbox like alteratives to infinite sustain, and while I tried and tried but couldn't get the effect that I was seeking with the infamous sustainer mod tutorial (I just got screaming feedback) it was the search that led me to PG when looking into these things...so, perhaps you contributed more than you think!

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Even if the driver is not exactly at the node, but close, the corresponding harmonic won't sound, simply because another one, that is close to its antinode will win.

As I imagine it should

It means that one harmonic, that has the best resonance conditions wins. And it's not necessarily the fundamental one.

No, rarely do the harmonics sound as the fundamental on any of these systems and I wouldn't expect them too. In playing the things I try and think a bit like a trumpet player say that only has three valves and the ability to "blow" different harmonics to get the various pitches and registers.

Still, it is a beautiful effect to have these other notes bloom out of the original...and generally they "work" as these harmonics are a part of the original sound of the vibrating string.

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A magnetic sustainer powered by the signal from the pickup, tends to amplify a single harmonic, eventually turning the sound into just a pure sine wave.

This sine wave philosophy has been very contentious in the last year, so I realize I am getting into dangerous waters to even comment. It was one of the last straws that broke the back of the main thread, spawning many of these related conversations that would have continued there...again, IMHO. However, it is a matter of "ideals" and "preferences" if this is the effect that is sought in my opinion.

The "sustainer" is simply another means to sound the instrument, like a pick or a bow on a violin. It has never been my goal to have a device that turns into a sine wave and made my opinion clear that it is the bits of the sound that are not a "pure sound wave" that give it character and so called "tone".

One could look at the vibrating string as a collection of vibrating modes...fundamental and harmonics, and these exist even if swamped by a harmonic and can easily be revealed by dampening at nodal or anti-nodal points along the length of the string, well after sounded...proving that these other modes of vibration still exist within a give note long after the initial strike of the string.

So, to have a sustainer that continues to excite these harmonic nodes, or even bloom them in preference to the fundamental vibration, is a beautiful thing and the subject of this thread no less.

There seems to be some confusion, perhaps all on my side, that you are talking about harmonics that sound the same note as the fundamental, and that is what you felt incredulous about being possible in your theory. As harmonics can be generated consistently with known sustainer systems, several on the market, it is obvious to anyone that it is indeed possible to make harmonics and for these to "bloom" out of the original fundamental. Octave or similar harmonics may indeed be unlikely with such a technology as is currently envisaged, but then if that is what you meant it might be an idea to clearly state that.

But as I say, i am a little confused...

Even if the driver is not exactly at the node, but close, the corresponding harmonic won't sound, simply because another one, that is close to its antinode will win.

"the" corresponding harmonic? Do you mean the octave or note of the original pitch. It can happen, but is rare, generally it is a higher order harmonic...my low "E" string will sound the note B and octave+5 higher than the original...the blooming effect is that for a while, both notes are apparent as the harmonic tone gradually takes over. Getting octaves only to sound would be difficult.

I did try things like bridging diodes and active half wave rectifiers and such, didn't go so far as an actual pitch shifter as I didn't have one at the time of these toyings, but with little success as far as getting specific harmonics to sound...but there may be something in that kind of approach. As always, at test rig to prove the theory or make it work is necessary if that is what is aimed for...talking about it wont really help a great deal till a concept is put into some kind of practical application or test...IMHO.

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PSW - in respect of the possibility that one harmonic "wins out", would having a multiple driver setup work? You could even vary the amplitude of each driver signal to create a modulated effect. Perhaps even varying the drive signal. How about an "insert" to the driver path to add an external stompbox modification to the signal, such as chorus, verb, etc?

Just mixing it up ;-0

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PSW - in respect of the possibility that one harmonic "wins out", would having a multiple driver setup work? You could even vary the amplitude of each driver signal to create a modulated effect. Perhaps even varying the drive signal. How about an "insert" to the driver path to add an external stompbox modification to the signal, such as chorus, verb, etc?

Just mixing it up ;-0

Thanks for the interest...

The sustainiac model C acoustic sustainer (the one that shakes the neck of the guitar physically with a transducer on the headstock) has this feature so that you could patch in effects.

Some are "interesting"...and there might be some potential...perhaps even being able to generate different harmonics...Col kind of did this with his 4-mode circuit that used filters. It's tricky because you are not just processing a sound, but trying to have that signal physically more a string in some novel way.

A tremolo for instance, has very little or any effect...the momentum of the string will sustain it though the loss of drive. SOme effects that change the pitch and delay, may not strike a resonant frequency that relates to the string vibration...some will ping off random harmonics like my work with flangers. FF and others like me have used compressors effectively to even out the response...AGC (automatic gain control). Auto wah or auto volumes have some appeal...especially for these blooming harmonics perhaps.

Distortions are ill advised...they can provide some compression, but they tend to add a bit of noise into the systems that are detrimental. They can work despite this, none of these circuits are particularly clean run this hard...but you will never get a string to actually physically vibrate in a square wave, no matter the signal driving it.

All these things can be extremely effective on the actual guitar signal and a sustainer can add new life to things like ultra long sweeps given the length of the notes. I did a demo song "siren sea" that is about somewhere that uses a pitch shifter in the middle section for a harmonized line. So, it is a real time sample at another pitch with all the harmonics and harmonic bloom of the sustainer which is kind of organic and as I recall some chorus like modulation as well...the result was a synthy organ like sound that was harmonized. There was another one around that used a choppy tremolo effect on the guitar...as the sustainer morphed from it's fundamental to it's harmonics and then yet another harmonic...that I can do on the lower pitches of my systems...it created a kind of "baba o'reily' or 'won't get fooled again' era who like sequenced synth like sound, as if each trem pulse was a different timbre and pitch related to the original. SO, there is plenty to play with there...but less os on the drive signal itself I fear.

It may be possible with a complete hex system to vary the amplitude to each driver or even to get better polyphony out of the things...but there are a lot of problems as described in another recent thread...driver interaction is one major one. Part of the problem is that generally, as conceived, all this would need to be in and power at the guitar itself...a tall order. The Moog guitar, perhaps promisise some of these kinds of things with it's on board step filtering and such...but little is truly known about this thing.

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edit.. question answered in a post above.

Edited by al s.
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The basic harmonic mode using a 180º phase inversion by swapping the wires is a little bit more complicated than most people give it credit for.

if you invert the signal, the driver cancels the fundamental, pushing the octave harmonic.

BUT then surely the octave harmonic then becomes the signal to the driver, and is in turn cancelled...

YES, otherwise the harmonic mode would stick at the octave.

BUT then surely if each time around, as soon as the next harmonic blooms it is cancelled, we soon get to such a high note we can't hear it?

AHA! that doesn't happen! WHY?

Now we are getting somewhere.

What is really happening - I think - is that the 180º phase shift is 180º across all frequencies due to the way it is obtained by swapping the connections. However, the drive circuit and combination of output cap and driver coil have a phase response that, while fairly flat over the desired range (82Hz to about 1200Hz), will quickly start veering off as the frequency increases. The note that the harmonic mode settles on is defined by the point at which the phase response of the circuit/cap/driver is more than 90º (and less than 270º) making the overall phase sum less than 90º (or greater then 270º).

This means that unfortunately, if you have a circuit with a very flat phase response (good for efficient sustaining) like mine, then the harmonic mode will generate unpleasantly high pitched harmonics, or ones that are so high, it can't drive them.

I think that one good way to create a controllable harmonic mode might be to in some way control this 'tipping point' where the response of the system cancels the 180º shift and halts the bloom effect.

What is the best way to do this ?

I don't know, but it isn't an approach that I have messed about with.

I did have some success with an all pass-filter, and a simple high pass filter, but I haven't yet managed to do a controllable effect where you can immediately notice the difference when you turn the knob... maybe a resonant filter will do it, or maybe tweaking the phase response in combination with a 180º shift will... (maybe a resonant filter is the best way to tweak the phase response...)

cheers

Col

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oops, forgot to add that of course, the physical phase gap between driver and pickup will also play a big part in this process - as the harmonic frequency rises, the pickup/driver gap becomes a bigger proportion of the cycle.

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I didn't want to get into that whole discussion about why the harmonics are not then canceled out and a chain reaction of ever increasing harmonics are generated.

There are a number of factors at play...the circuit may not be able to have the fidelity to produce much of a cancellation effect at such high frequencies, the higher harmonics will be progressively lower in the mix, the physical location of the source and driver might be a fairly big factor. I'm just glad that in general it does not. Perhaps, with an ideal situation you would produce a muting 'anti-sustainer' with the drive reversed...it was something of an amazement to find that the harmonics could be generated by connecting the signal, drive or magnets back to front!!!

I do recall having problems with high harmonics...till I realized that the strings were vibrating, but the amp I was testing the thing on could not make sounds so high. As it is a harmonic on the very highest frets can be almost painfully high...think of the old EVH horse whiny kind of effect that was popular for a bit...holding such notes might set off the neighbors dogs!

Some of the quirks of this device I'm actually grateful for myself...that it works at all is enough for most!

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