Some interesting reading

[Mark Hammer]

Not sure if folks had stumbled onto this year-old thesis. Haven't read it yet, but any time someone tries to present something near and dear to us in an academic format, there is sure to be an intriguing quarter twist.

http://puhep1.princeton.edu/~mcdonal..._77_148_09.pdf

[guitician]

If anyone is interested in the title of the PDF it's "Modeling the Magnetic pickup of an Electric Guitar". I'm thinking that "modeling" always means compromising tone in some way. The magic of plugging straight in and having 50khz of bandwidth flowing all the subtle dynamics of what is really happening is what made the instrument great. I've plucked 12 fret harmonics and watched the pickups output on a scope and it's very sinusoidal. I guess that is because of the "vertical only" motion of the string when plucked this way. At the other end of that analysis, is when a player "Digs in" and drives the distorting amp with an also distorted guitar signal. Interesting

[David Schwab]

I think they mean modeling in the sense of coming up with a model of the pickup, in regards to how it works. Not like software amp modeling.

I don't think any guitar amp goes to 50kHz, and certainly speakers don't. I doubt there is much information in the guitar's signal up that high either, if any.

As far as amp modelers.... Digidesign has a really good one called Eleven. You would be hard pressed to tell the difference between a recording done with that and the real thing.

Dave Navarro did a demo uses it as a live amp setup. Eventually they will be perfect.

[salvarsan]

I'm thinking that "modeling" always means compromising tone in some way.

When a marketroid says 'modeling', they actually mean "a simulation as a rationale to extort more money for a uninteresting product."

When a scientist says 'modeling', they mean "to construct a simplified system for detailed analysis so as to improve the understanding of complex systems."



So, if the physics guys get a peer-reviewed article into a journal, it's reasonably true as far as it goes.


They say that vertical string motion produces more output than horizontal string motion. The horizontal output is 24dB down on the fundamental and
anywhere between 6 and 30 dB down out to the 8th harmonic.

This is good to know. It means that if you hold your plectrum/pick vertically like a scalpel and parallel to the string, you will emphasize the fundamental.
Eric Johnson does exactly that since his weapon of choice, the Arbiter Fuzz Face, sounds gritty with any ordinary right hand technique.

Conversely, if you hold the plectrum at non-parallel angle to the string (which is almost always), you get more pick-chirp at the beginning and more harmonics afterwards.

Well, duh.

The article does not model the magnet or the pickup coil so they aren't telling us anything germane to building pickups.

-drh

[guitician]

I don't think any guitar amp goes to 50kHz, and certainly speakers don't. I doubt there is much information in the guitar's signal up that high either, if any.

Ah! But it's analog, and the 50khz signal is still there none the less, though very small in relation to the fundamental. Speakers also respond higher than spec'd and if you set an EQ to push the higher frequencies you'll here their effect.

[David Schwab]

Ah! But it's analog, and the 50khz signal is still there none the less, though very small in relation to the fundamental. Speakers also respond higher than spec'd and if you set an EQ to push the higher frequencies you'll here their effect.

That all depends on the circuitry. Just because it's analog doesn't mean a thing. You don't want to reproduce RF signals so that stuff is often filtered out. And what's the highest EQ you have? I have 16K on a 10 band EQ, and I can't even hear that. No EQ goes up to 50K.

Same with speakers... look at a frequency graph on speakers and you can see the drop off.

Same is true of guitar pickups.

The point is moot anyway since you can't hear much over 18kHz or so.

[guitician]

That's the thinking of all the audio engineers that started making amps that sounded like crap, but sound great on paper. You don't hear the notes above 18khz, but they mix in with the signal and effect it though. Wide-band response and stability are two different things. Fast caps will make an amp sound better, but shouldn't have made any difference on paper.

[salvarsan]

That all depends on the circuitry. Just because it's analog doesn't mean a thing. You don't want to reproduce RF signals so that stuff is often filtered out. And what's the highest EQ you have? I have 16K on a 10 band EQ, and I can't even hear that. No EQ goes up to 50K.

Bandwidth is not the same as accuracy.

Instruments generate overtones that are in-phase with the fundamental
frequency. A brick-wall filter near 1/2 the sample frequency often causes
audible phase shift.

Usually, if you want phase coherency on impulse sounds (such as snare,
cymbals, triangles and square waves), your signal chain should sample at
10x the maximum audible frequency.

For us increasingly decrepit rockers, the audible ceiling is closer to 10kHz
suggesting a 100kHz sample rate to minimize phase distortion artifacts.

This is why we get 192kHz sampling of audio (but no faster) -- the benefits
of phase coherency above 19kHz reproduction are irrelevant even with
excellent hearing.

-drh

[RedHouse]

That's the thinking of all the audio engineers that started making amps that sounded like crap, but sound great on paper. You don't hear the notes above 18khz, but they mix in with the signal and effect it though. Wide-band response and stability are two different things. Fast caps will make an amp sound better, but shouldn't have made any difference on paper.

No that's the thinking of armchair technician guys that can't hear the difference. It's the audio engineers that can hear a .1uF cap across a 47uF electrlytic (ala, Neve). Freq's above hearing hetrodyning into the sound isn't a really good thing.

I'd disagree about those upper freq's making the sound better, most of what we call the "good sounding" amps have upper freq's shunted in-circuit. (Plate bypas caps etc). Bandwidth limitation is not an evil thing, it's appropriate in most cases and specially with instrument amps it's a time-proven advantage.

[David Schwab]

...A brick-wall filter near 1/2 the sample frequency often causes audible phase shift.

Right, but he was talking analog guitar amps. They don't go up to 50K in any meaningful way.

And I realize that high frequency content that is often filtered out in digital recordings (especially older ones) carries phase information.

[David Schwab]

I'd disagree about those upper freq's making the sound better, most of what we call the "good sounding" amps have upper freq's shunted in-circuit. (Plate bypas caps etc). Bandwidth limitation is not an evil thing, it's appropriate in most cases and specially with instrument amps it's a time-proven advantage.

That's what I was getting at.

[guitician]

No that's the thinking of armchair technician guys that can't hear the difference. It's the audio engineers that can hear a .1uF cap across a 47uF electrlytic (ala, Neve). Freq's above hearing hetrodyning into the sound isn't a really good thing.
.

For sound reproduction maybe. This is all I'm getting at....If you let everything that is on the wire coming out of the guitar through to the speaker, no matter how far down in db it is, you will be playing the most of what the electric guitar has to offer. There, nuff said.

[Mike Sulzer]

David,

From the paper:

"The magnetic field created by a permanent magnet and a
ferromagnetic wire can be modeled by treating the magnet as
a pair of disks of opposite magnetic charge and the ferromag-
netic wire as a series of infinitesimally wide cylindrical mag-
nets."

I am not the only one saying that the string is magnetized in the presence of the pickup's permanent magnet. Note that the model is simplified ("This model can be understood by undergraduate students and provides an excellent learning tool due to its straightforward mathematics and intuitive algorithm."), but it does catch the basic idea.

The authors assume cylindrical permanent magnets, so they are limiting the model to something like Fender single coil pickups. It would apply in an approximate way to steel pole pieces magnetized by the usual traverse-magnetized bar magnet.

Also, we have discussed before that the response is much greater to vertical string motion than horizontal motion in regard to some of those patents you refer to, the ones making the false claims about the horizontal motion.

[Mike Sulzer]

Not sure if folks had stumbled onto this year-old thesis.
http://puhep1.princeton.edu/~mcdonal..._77_148_09.pdf

I thought the most interesting part is the predictions of how much distortion there is in the pickup up process. This appears to be mostly due to the non-linear variation of the magnetic field with distance from the pole piece.

The results are for 4 mm and 8 mm above the pole piece. There is more distortion at the lower height. 8 mm is way too high. 4 mm is about 5/32 inch, which still seems a bit high. Would the distortion be even greater at lower spacings? I suspect not because the way the field varies near the magnet.