Inductive balancing of cores and windings

[fieldwrangler]

I don't think there's much in audio that can't be simulated, seeing as how high quality digital reproductions sound damn good to me. In the practical worlds of sampling & convolution I think many decisions are often made about streamlining and approximating the data that might sometimes be responsible for the results feeling less "multidimensional."

This having been said, here's an excerpt from the introduction included in my current business plan. Truth be told, I don't think that there's anything "simple" at all about the way in which amps & speakers process a signal but you'll get the idea:



Electric guitars and basses rely on one or more pickups to capture the sound of strings, essentially serving as the primary interpreter of string behavior. These transmit an analog electrical signal to the next device in an extremely variable chain, which could be as simple as an amplifier with speakers or as complex as a dozen signal processors feeding a recording interface. However, the initial input, as represented by the pickup, has intrinsic dynamic elements whose character persists throughout this chain and therefore form a representation of the player’s intent which remains central to the final sound. Because of this, the pickup, offering a choice of response characteristics coming directly from the source, is always of primary importance to guitarists.

FWIW -

Bob Palmieri

[Antigua]

Do you think that the magnetic characteristics you are discussing (remanence, coercivity, eddy losses, etc.) of the poles, magnets, magnetic structure, etc. in the pickup are nonlinear in the interaction between string and magnetic field, and complex coil impedance, and therefore not easily reproducible by downstream signal processing, or are they in your opinion, linear filtering effects that can be separated out by magnetic circuit, coil effects, etc. which can just be added in or changed by X stages of analog or digital filters downstream?

There are two different issues to consider, a) how the core material effects inductance, and b) how the magnetism causes the string to relate to the pickup. I think "b" would be harder to simulate down the line, for example, digitally attempting to raise or lower the pickup, or turn the pickup sideways, because I suspect that would result in different information being produced, but with respect to "a", the material's contribution towards inductance, that aspect doesn't create or destroy information, it just changes the amplitudes of the information, and so I don't see why that aspect couldn't be modified down the line. I think this is the principle on which the new Fishman Fluence pickups operate; take a flat signal and shape into into a peaky one.

The caveat is that beyond the resonant peak, the amplitude drops sharply, so eventually the higher harmonics descend into the the noise floor, and that does mean information is lost, so you'd want to have a pickup with a real high resonant peak if your intention was to digitally simulate other coil configurations. It therefore might be difficult to make an AlNiCo 2 digitally sound like an AlNiCo 5 because if the AlNiCo 5 produces a higher resonant peak, the digital simulation would want to emphasize harmonic information that the actual AlNiCo 2 had already flushed down the drain.

My own question would be; when you raise and lower a pickup, or change the Gauss of the a magnet, is different information being produced by the guitar, or is the change strictly in terms of amplitude, or the "amount" of information being produced by the guitar? Since magnetic field lines extend to infinity, my guess is that the information remains the same, so long as the pickup is in a fixed spot along the guitar string (and can't twist around like a Turner Model 1), with perpendicular orientation to the strings.

[charrich56]

Thanks for the great responses, guys. So here's maybe another question -- ScottA for example, has done a lot of analysis on how the mag circuit , eddies in the pole piece, etc. affects the resonance peak width and shape with a given coil, in circuit. But if you are researching the real effect of the magnetic circuit and string interactions, don't we want to get the coil resonance out of the way completely (e.g. a low impedance coil with preamp) for this investigation? This relates a bit to Antigua's comment just above.

What I am suggesting is that some of the effects on resonance behavior (Q/bandwidth, shape of the peak) that you might be chasing with different magnets, pole material, etc. might be partially artifacts because of interaction with that particular coil and downstream electrical circuit that you held constant, and you haven't extracted the real predictive knowledge of <just> the magnetic circuit that you would need to engineer another pickup with a different coil. (windings, gauge, etc.)

You may not need to chase the rabbit all the way down the hole though. But we are really chasing different rabbits. There's a "vintage magic mojo" rabbit, a "vintage plus modern plus new stuff" rabbit, and a "completely condenser mic flat, do it with DSP" rabbit. This thread is relevant to all three types of rabbit chasers I think.

[Mike Sulzer]

Do you think that the magnetic characteristics you are discussing (remanence, coercivity, eddy losses, etc.) of the poles, magnets, magnetic structure, etc. in the pickup are nonlinear in the interaction between string and magnetic field, and complex coil impedance, and therefore not easily reproducible by downstream signal processing, or are they in your opinion, linear filtering effects that can be separated out by magnetic circuit, coil effects, etc. which can just be added in or changed by X stages of analog or digital filters downstream?

All that we are dealing with are aspects of Maxwell's equations. These equations, in their vacuum form are linear. Add magnetic materials, and there are nonlinearities. However, with pickups, we operate with small perturbations about an initial state, and we are very very close to completely linear behavior. However, this does not mean that everything is easily exactly simulated with the usual digital filters. The effect of the pole pieces involves the magnetic induction of energy from one circuit into another: mutual inductance. These effects are more complicated than the usual RLC effects that people deal with.

[fieldwrangler]

The shape of that response is determined by the core, and specifically how the magnetic flux gets "filtered" due to eddy current effects in the core.

It's about how the flux gets filtered through and by the core material.

Stay tuned. I will lay out my model in some detail with supporting data. I'm sure you'll be interested and have a lot to say about it.

I must say, my current experiences point in a direction that really resembles what you're saying here.

[ScottA]

I must say, my current experiences point in a direction that really resembles what you're saying here.

That's because it's correct. ;-)