Video on Seymour Duncan resonant frequency testing

[timtam]

Premier Guitar has just released a new Seymour Duncan factory tour video (50 minutes long). From about 37 minutes in, it shows what is probably the most detailed video I've seen of how any major pickup manufacturer tests pickups (although that isn't saying much). It's with Kevin Beller, SD's VP of Engineering and New Product Development.

Like the earlier less detailed PRS video, it's a custom procedure. But the exact details were not 100% clear to me.

Their process for resonant frequency uses the signal generator in an Amber 3501a Distortion Analyser (stock photo below) to sweep frequencies. He's shown adjusting that manually with the Frequency knob. Since they're only using the signal generator, only the connected left Output cable is presumably relevant (not the Monitor Input and Distortion connections close to the middle front panel). But I can't trace exactly where that cable is going - maybe to the 'black box' (see below).

The pickup is wired directly to a custom silver 'black box' instrument shown in the video, that he doesn't explain (30-year old "clanky fixture"). Maybe there's an exciter there somewhere that we can't see ? There's a cable coming out of the silver box labelled 'to chart recorder' - presumably the pickup output that is going to the Rhode RTB2004 oscilloscope (below).

It appears to be a semi-manual process to find the resonant frequency. For the test pickup here he says that's 4.1 kHz, which is showing on the oscilloscope display, along with the sine wave that is presumably the signal being measured. So he may just be looking for the maximum P-P amplitude on the oscilloscope as he manually sweeps the frequencies ? Any other insights welcome.

He says they also measure inductance, the Q factor, and magnet gauss. With that large tray of same-pickup models on his bench, it may also indicate that they test for variability in the measured specs.

This all shows that SD could publish resonant frequency, inductance and Q factor if they wanted to.

He also shows a semi-automated 'strum tester' guitar with a spring-loaded strumming fixture (below). They use that to measure the pickup's output strength, again on the oscilloscope (average of 10-15 readings).

[antigua]

Thanks for sharing, that's interesting. It also just cool to see an electronic good being manufactured in America this day and age. 

They way they find the peak frequency is almost exactly how I used to do it, plug the exciter into a signal generator, turn the frequency up and watch the oscilloscope for the voltage peak, then just write down the frequency. I think the black box might just be putting a resistor across the pickup in order to measure the impedance, like this but in a  shielded enclosure  guitarnuts2.proboards.com/thread/7775/pickups-resonant-peak-usb-oscilliscope , I can't imagine what more would be required in between the pickup and the scope.

Hearing him talk about AlNiCo from the perspective of a pickup mfg was interesting also. I'm glad to hear they take the details into consideration, although when it comes to actual production, it's hard to say whether or not that detail takes a back seat to cost efficiency. Would they order a special formulation of AlNiCo just to create a perfect Joe Bonamasa pickup replica?

That strumming device looks well thought out, and I wonder why they do for the plectrum, because I made a setup similar to this, and I got a lot of variation in the outcome depending on the plectrum type and how it was attached to the arm. 

It's annoying to hear that they collect data such as inductance and Q factor but apparently refuse to share it.  It just goes to show the adversarial relationship between the pickup makers and the customers which people have hated on me for in the past, but in both the case of PRS and Seymour Duncan, evidently they have the info, but put customers in a position of having to choose a product without the benefit of that info. I bet they would try to protect it as a trade secret if it were so trivial to gather with an LCR meter. 

[tonyfg]

Hi guys, brand new to building and testing pickups. Some great info on here. I watched that video and it’s great to get an insight how the big guys do it. As far as testing goes most of the measurements like RCL is all ok and easy enough to find. I’m honestly still working on how to properly interpret this kind of data for practical purposes and I honestly need to do a lot more testing and reading. He mentioned that the strum test was to test output. On his website he shows a pretty crude scale for output but also a tiny bar graph for Bass Middle Treble, I wondered how exactly the proper figures to produce these would be derived in order to have a purely practical way for comparison. Thanks.

[antigua]

Jan 25, 2024 11:00:51 GMT -5 tonyfg said:

Hi guys, brand new to building and testing pickups. Some great info on here. I watched that video and it’s great to get an insight how the big guys do it. As far as testing goes most of the measurements like RCL is all ok and easy enough to find. I’m honestly still working on how to properly interpret this kind of data for practical purposes and I honestly need to do a lot more testing and reading. He mentioned that the strum test was to test output. On his website he shows a pretty crude scale for output but also a tiny bar graph for Bass Middle Treble, I wondered how exactly the proper figures to produce these would be derived in order to have a purely practical way for comparison. Thanks.

The bass/middle/treble values are made up, they have to be because a guitar pickup is one or two coils of wire with no other circuitry ahead of the connection cable. But actually there is other circuitry in the form of unwanted resistance, inductance and capacitance, and it's because of all three that the pickup has a resonant peak frequency and a low Q factor. If it were possible to make a pickup with no R, L and C, there would be technical upsides, like a more broad frequency response and less susceptibility to noise, and that's realized with low impedance pickups and active pickups. Fishman Fluence can claim to have bass mids and treble because they actually do fit their active pickups with a filter circuit, so that they can offer several sound profiles with one pickup. Virtually any passive guitar pickup with a DC resistance over 6k ohms will have a resonant peak that is audible to the ear, and what distinguished almost all the passive pickups on the market is little more than the frequency that high end content is rolled off. More inductance = less treble. 

Another reason you can't characterize a pickup as having bass middle and treble is because that depends so much on where the pickup is positioned in the guitar. Any pickup in the neck position will have a lot more proportionate bass than any pickup in the bridge position. A guitar pickups functions as a filter, but for marketing purposes, pickup vendors try to portray them as the source of the sound, which is actually the guitar strings. 

As for strumming, people don't realize how hard it is to strum consistently. It sounds mostly consistent to our ear, but we're often looking for a difference that is much smaller than our ability to strum consistently. Not only do you pick with more or less force, but hit the strings with different angles of attack, and pluck in slightly different places, which all add together to make for a different result, strum for strum. But that's why guitar sounds alive and synthesizer music sounds robotic. It's very hard to play guitar in a way that seems robotic, and that's good for music but a problem for pickup or general guitar testing. That's probably why there is so much magical thinking around guitar, it's very difficult to objectively test guitars without fancy equipment. 

For practical comparison, I just need to see the inductance of a pickup most of time time, the treble response is inversely proportionate to the inductance. The perception that a pickup has a lot of bass or mids is just an byproduct of lacking some amount of treble. For a given style of pickup, the amount of resistance represented by eddy currents will be inherent to the style of pickup, Fender single coils very low, anything with steel pole pieces will have a higher resistance, and therefore a low Q factor. That's why Fender uses 250k pots, but most other pickups are paired with 500k pots, it's a lot more trivial than inductance.

The fact that Seymour Duncan provides BMT, but not inductance, tells me that they want customers to be confused. It makes it easier for them to offer new products that are very similar to existing products, without having to make it so obvious, and it creates the impression that the creative input of their product designers is more substantial than it really it. Almost all the pickup makers want to be seen as artisans, but there's just not that much dynamic and dimension to a coil of wire mounted to some kind of frame. 

[tonyfg]

Thanks Antigua, great answer spot on!

[timtam]

AFAIK none of the few pickup makers that provide some form of "EQ chart" (bass/mids/treble) on their pickup product pages has described how they derive it. I can't think of an objective way to get from a proper bode plot to such a chart. If there was one it would presumably need to assign a weighting to bass and mids in relation to the height and frequency of the (treble) resonant peak - the only things that pickup makers can really control. But I'm guessing such EQ charts are more likely to come from something like a group of staff sitting around a (unspecified) guitar/amp with a given pickup installed, saying "Now what do we give the mids ? I reckon they get a '3'. Any advance on '3' ?"

[Wim]

None of their competitors offer those numbers, and no consumers would know what it means except for like 10 people on this forum. Bass Mid Treble approximations are better than what anyone else offers, and it doesn't give their competitors an edge. So many pickup makers don't have any clue what a resonant peak is, they just think that Formvar gives you are airier tone or whatever nonsense.

If you start distilling the characteristics of your pickups to measurable values, you can't charge as much either. Keeping things hand-wavy keeps the prices higher.

[antigua]

Feb 9, 2024 13:10:34 GMT -5 Wim said:

None of their competitors offer those numbers, and no consumers would know what it means except for like 10 people on this forum. Bass Mid Treble approximations are better than what anyone else offers, and it doesn't give their competitors an edge. So many pickup makers don't have any clue what a resonant peak is, they just think that Formvar gives you are airier tone or whatever nonsense.

If you start distilling the characteristics of your pickups to measurable values, you can't charge as much either. Keeping things hand-wavy keeps the prices higher.

I think the best companies have faith in their customers. I think if Seymour Duncan presumed their customers were smart, a market of smart customers would open up, and they would dominate that market for as long as their competitors played it business as usual. Instead, they underestimate guitarists out of fear and a lack of faith. I think it's still possible to sell a wide offering of pickups, even if their differentiation is more technical and less Lord of the Rings monsters. There's also lots of aesthetic and color options to set them all apart.  

Speaker companies, especially Jensen and Celestion, provide lots of technical specs for their speakers, many specs with have parallels to these tech specs of pickups that we talk about, such as their electrical resonance and impedance.  

With rock and roll no longer being the youth cultural keystone that it once was, guitar is being looked at more as an instrument, and less like Thor's magic hammer for pounding out power chords. I think the anti-intellectual perception of guitar and pickups is on the way out. 

[woundup]

Feb 11, 2024 3:26:49 GMT -5 antigua said:

Feb 9, 2024 13:10:34 GMT -5 Wim said:

None of their competitors offer those numbers, and no consumers would know what it means except for like 10 people on this forum. Bass Mid Treble approximations are better than what anyone else offers, and it doesn't give their competitors an edge. So many pickup makers don't have any clue what a resonant peak is, they just think that Formvar gives you are airier tone or whatever nonsense.

If you start distilling the characteristics of your pickups to measurable values, you can't charge as much either. Keeping things hand-wavy keeps the prices higher.

I think the best companies have faith in their customers. I think if Seymour Duncan presumed their customers were smart, a market of smart customers would open up, and they would dominate that market for as long as their competitors played it business as usual. Instead, they underestimate guitarists out of fear and a lack of faith. I think it's still possible to sell a wide offering of pickups, even if their differentiation is more technical and less Lord of the Rings monsters. There's also lots of aesthetic and color options to set them all apart.  

Speaker companies, especially Jensen and Celestion, provide lots of technical specs for their speakers, many specs with have parallels to these tech specs of pickups that we talk about, such as their electrical resonance and impedance.  

With rock and roll no longer being the youth cultural keystone that it once was, guitar is being looked at more as an instrument, and less like Thor's magic hammer for pounding out power chords. I think the anti-intellectual perception of guitar and pickups is on the way out. 

I think it's time for me to learn more about this stuff. I finally went over one of your analysis, of the Epiphone 57CH pickup, and it's all extremely interesting. I've never looked into pickups this much, even after all the stuff youve posted at ST since I've been there. But I think it's time to start learning. Now that I've started buying better pickups, I've become a lot more interested in all of it. I know you've tested Seth Lovers and 59s so I'll have to find your analyses and see what I can learn!

Edit: apparently your analyses are quite popular. If you type "Antigua pickup" into Google, it finishes it with "...analysis". That's saying a lot! Nice job!

[antigua]

Feb 11, 2024 12:18:31 GMT -5 woundup said:

I think it's time for me to learn more about this stuff. I finally went over one of your analysis, of the Epiphone 57CH pickup, and it's all extremely interesting. I've never looked into pickups this much, even after all the stuff youve posted at ST since I've been there. But I think it's time to start learning. Now that I've started buying better pickups, I've become a lot more interested in all of it. I know you've tested Seth Lovers and 59s so I'll have to find your analyses and see what I can learn!

Edit: apparently your analyses are quite popular. If you type "Antigua pickup" into Google, it finishes it with "...analysis". That's saying a lot! Nice job!

That's funny. I often use Google to look up my old info. That's one of the reasons I post it on the internet. 

This article about how pickups work is pretty good www.buildyourguitar.com/resources/lemme/ , also Manfred Zollner's work is great gitec-forum-eng.de/wp-content/uploads/2020/09/poteg-5-magnetic-pickups-a.pdf  

At some point AI will ingest Manfred Zollner's work and AI will understand how pickups work better than any human.

[ms]

Feb 11, 2024 16:47:49 GMT -5 antigua said:

Feb 11, 2024 12:18:31 GMT -5 woundup said:

I think it's time for me to learn more about this stuff. I finally went over one of your analysis, of the Epiphone 57CH pickup, and it's all extremely interesting. I've never looked into pickups this much, even after all the stuff youve posted at ST since I've been there. But I think it's time to start learning. Now that I've started buying better pickups, I've become a lot more interested in all of it. I know you've tested Seth Lovers and 59s so I'll have to find your analyses and see what I can learn!

Edit: apparently your analyses are quite popular. If you type "Antigua pickup" into Google, it finishes it with "...analysis". That's saying a lot! Nice job!

That's funny. I often use Google to look up my old info. That's one of the reasons I post it on the internet. 

This article about how pickups work is pretty good www.buildyourguitar.com/resources/lemme/ , also Manfred Zollner's work is great gitec-forum-eng.de/wp-content/uploads/2020/09/poteg-5-magnetic-pickups-a.pdf  

At some point AI will ingest Manfred Zollner's work and AI will understand how pickups work better than any human.

User
What are the details of the magnetization induced in a guitar string by a pickup magnet?


ChatGPT: "When a guitar string vibrates above a pickup magnet, it induces a changing magnetic field according to Faraday's law of electromagnetic induction. This changing magnetic field induces an electric current in the coil of wire wrapped around the pickup magnet. The induced current carries information about the vibration of the string and is then amplified and sent to the amplifier, producing sound.

The details of the magnetization induced in the guitar string by the pickup magnet depend on several factors:

Magnetic Field Strength: The strength of the magnetic field generated by the pickup magnet influences the amount of magnetization induced in the guitar string. Stronger magnets can induce stronger currents in the coil.
Distance from the String: The proximity of the pickup magnet to the guitar string affects the strength of the induced magnetic field. Closer proximity typically results in stronger induction.
Material and Gauge of the String: Different materials and thicknesses of guitar strings will have varying responses to the magnetic field. For instance, steel strings are more responsive to magnetic fields than nylon strings due to their ferromagnetic properties.
String Motion: The movement of the guitar string itself affects the changing magnetic field. As the string vibrates, the magnetic field it interacts with changes accordingly, inducing varying levels of magnetization in the string.
Coil Design and Number of Turns: The design of the coil wrapped around the pickup magnet, as well as the number of turns of wire, can affect the sensitivity and response of the pickup to the induced magnetic field.
Overall, the process involves the interaction between the vibrating guitar string and the magnetic field generated by the pickup magnet, resulting in the induction of an electric current in the pickup coil, which is then amplified and converted into sound."

Let's check the progress in understanding.  First, it is a voltage that is induced, not a current. The current flows because the electrical elements of the circuit are excited by a voltage.  This program loves to propagate  errors; it has not yet learned how to distinguish repetition of incorrect answers from proper understanding?  Why? It could look up Faraday's law and fix this error, even if it is still decades away from actually understanding physics.

The rest of the answer is very shallow.  It does not understand that the field inside the string has a spatial pattern that is important to understanding.  It must have ingested some of Zollner's work (and several others'). but it selects the shallow discussions, apparently because it weights frequent repetition over careful logical analysis.  I do not understand why; it should be able to detect material that contains logical deductions as well as facts (or statements that appear to be facts). Apparently it is mainly just a language analyzer.

[ms]

"User
Faraday's law says voltage is induced. Why do you say current?

ChatGPT
You're correct; I misspoke. Faraday's law states that a changing magnetic field induces a voltage, not a current, in a coil of wire. This induced voltage, in turn, causes an electric current to flow in the circuit if there is a closed loop.

So, to clarify, when a guitar string vibrates above a pickup magnet, it induces a changing magnetic field, which in turn induces a voltage in the coil of wire wrapped around the pickup magnet. This induced voltage drives an electric current in the circuit connected to the pickup, which is then amplified and converted into sound. Thank you for pointing out the error."

So it can be corrected.  I wonder if it will remember this correction.

[ms]

"User
The induction of magnetization in the string by the pickup magnet has an important spacial pattern, in particular a reversal of direction over the pole piece. Why have you not discussed this?

ChatGPT
You're correct; I didn't address the spatial pattern of magnetization induced in the string by the pickup magnet, particularly regarding the reversal of direction over the pole piece. Let's delve into that further:

In a typical guitar pickup design, there are one or more pole pieces placed beneath the strings. These pole pieces are regions of concentrated magnetic flux produced by the pickup magnet. When a guitar string vibrates above these pole pieces, it interacts with the magnetic field in a spatially varying manner.

At the pole piece, where the magnetic flux density is highest, the magnetization induced in the guitar string reaches its maximum intensity. As the string moves away from the pole piece, the strength of the induced magnetization decreases. Importantly, when the string crosses over the pole piece, the direction of the induced magnetization reverses.

This reversal of magnetization direction is due to the changing orientation of the magnetic field as the string moves across the pole piece. It's a crucial aspect of how the pickup senses the vibration of the string. The changing magnetic field induces alternating current in the pickup coil, which corresponds to the vibration pattern of the string. This alternating current is then amplified to produce sound.

The spatial pattern of magnetization induced in the string, including the reversal of direction over the pole piece, contributes to the unique tonal characteristics of different pickup designs. For example, pickups with staggered pole pieces may provide a more balanced response across the strings, while pickups with flat pole pieces might emphasize certain frequencies."

This seems more like BS rather than understanding.

[ms]

"User
You are correct that the flux density from the pickup magnet reaches its maximum density over the pole piece, but since the magnetization reverses direction over the pole piece, the magnetization is not maximum there but rather goes through zero. It does, however, reach a maximum near the edges of the pole piece or just outside of it.

ChatGPT
You're absolutely correct, and I appreciate the clarification. I apologize for any confusion. The magnetization induced in the guitar string does indeed reach its maximum near the edges of the pole piece or just outside of it, rather than directly over the pole piece where it reverses direction.

This phenomenon occurs because the magnetic flux density is highest directly over the pole piece, but the magnetization induced in the string itself goes through zero at that point due to the reversal of direction. Near the edges of the pole piece, where the magnetic field is still strong but the direction is consistent, the induced magnetization reaches its maximum.

This spatial pattern of magnetization, with its reversal over the pole piece and maximum near its edges, is crucial for the pickup's functionality and contributes significantly to the unique tone and response characteristics of different pickup designs. Thank you for the clarification."


So this is just complete BS in this sense:  It is assuming I am correct, and trying to agree in an intelligent seeming way.  Kind of disappointing. It does not appear that chatGPT understands guitar pickups at all.  It is all verbal smoke and mirrors.

[antigua]

I'm still impressed that it can BS as well as it does. Is it really worse than the BS pickup makers put out?

A lot of the mistakes become apparent only after you connect the dots, like the distinction between whether voltage causes current or current causes voltage. A lot of times Chat GPT has the ability to come up with the right answer after you inform it of it's mistake. There has also been talk about Chat GPT being "lazy", and this does seem like laziness. I don't understand how the algorithms work, but I wonder if the mistakes are due to a lack of self-checking. Like when it makes up facts, why can't one Chat GPT take the answer of another Chat GPT, and interrogate it's answer before it presents to the end user? 

Hopefully at some point it will see Manfred Zollner's work, and we can prompt "according to Zollner..."

[ms]

Feb 12, 2024 11:22:56 GMT -5 antigua said:

I'm still impressed that it can BS as well as it does. Is it really worse than the BS pickup makers put out?

A lot of the mistakes become apparent only after you connect the dots, like the distinction between whether voltage causes current or current causes voltage. A lot of times Chat GPT has the ability to come up with the right answer after you inform it of it's mistake. There has also been talk about Chat GPT being "lazy", and this does seem like laziness. I don't understand how the algorithms work, but I wonder if the mistakes are due to a lack of self-checking. Like when it makes up facts, why can't one Chat GPT take the answer of another Chat GPT, and interrogate it's answer before it presents to the end user? 

Hopefully at some point it will see Manfred Zollner's work, and we can prompt "according to Zollner..."

I really like  "according to Zollner...".  I think of prompting with this as a way to get it to go looking in Zollner's book.  Not sure if it will delve into translated PDF files.  The translations are excellent, but it still might find some way to get confused.  I need to think of the right "hook" to introduce this.

[ncblue]

Feb 12, 2024 12:38:37 GMT -5 ms said:

Feb 12, 2024 11:22:56 GMT -5 antigua said:

I'm still impressed that it can BS as well as it does. Is it really worse than the BS pickup makers put out?

A lot of the mistakes become apparent only after you connect the dots, like the distinction between whether voltage causes current or current causes voltage. A lot of times Chat GPT has the ability to come up with the right answer after you inform it of it's mistake. There has also been talk about Chat GPT being "lazy", and this does seem like laziness. I don't understand how the algorithms work, but I wonder if the mistakes are due to a lack of self-checking. Like when it makes up facts, why can't one Chat GPT take the answer of another Chat GPT, and interrogate it's answer before it presents to the end user? 

Hopefully at some point it will see Manfred Zollner's work, and we can prompt "according to Zollner..."

I really like  "according to Zollner...".  I think of prompting with this as a way to get it to go looking in Zollner's book.  Not sure if it will delve into translated PDF files.  The translations are excellent, but it still might find some way to get confused.  I need to think of the right "hook" to introduce this.

Hi guys, I read this today and thought I would give this a try, I went on Bing's AI and asked it to look into "Physics of the Electric Guitar" by Zollner and gave it the link to the english translation.  It was a question relating to the design of bridges not pickups, but none the less it's said it could not look into the book due to copyright. I did send a note to Dr. Tilmann Zwicker on this for his information. Should it be turned loose to AI?  

[antigua]

Feb 14, 2024 20:31:59 GMT -5 ncblue said:

Feb 12, 2024 12:38:37 GMT -5 ms said:

I really like  "according to Zollner...".  I think of prompting with this as a way to get it to go looking in Zollner's book.  Not sure if it will delve into translated PDF files.  The translations are excellent, but it still might find some way to get confused.  I need to think of the right "hook" to introduce this.

Hi guys, I read this today and thought I would give this a try, I went on Bing's AI and asked it to look into "Physics of the Electric Guitar" by Zollner and gave it the link to the english translation.  It was a question relating to the design of bridges not pickups, but none the less it's said it could not look into the book due to copyright. I did send a note to Dr. Tilmann Zwicker on this for his information. Should it be turned loose to AI?  

Thanks for trying that and contacting Tilmann Zwicker. I'm sure he'd like for it to be ingested for AI, he translated it in order for the work to reach a wider audience. 

[woundup]

Feb 12, 2024 10:01:47 GMT -5 ms said:

"User
You are correct that the flux density from the pickup magnet reaches its maximum density over the pole piece, but since the magnetization reverses direction over the pole piece, the magnetization is not maximum there but rather goes through zero. It does, however, reach a maximum near the edges of the pole piece or just outside of it.

ChatGPT
You're absolutely correct, and I appreciate the clarification. I apologize for any confusion. The magnetization induced in the guitar string does indeed reach its maximum near the edges of the pole piece or just outside of it, rather than directly over the pole piece where it reverses direction.

This phenomenon occurs because the magnetic flux density is highest directly over the pole piece, but the magnetization induced in the string itself goes through zero at that point due to the reversal of direction. Near the edges of the pole piece, where the magnetic field is still strong but the direction is consistent, the induced magnetization reaches its maximum.

This spatial pattern of magnetization, with its reversal over the pole piece and maximum near its edges, is crucial for the pickup's functionality and contributes significantly to the unique tone and response characteristics of different pickup designs. Thank you for the clarification."


So this is just complete BS in this sense:  It is assuming I am correct, and trying to agree in an intelligent seeming way.  Kind of disappointing. It does not appear that chatGPT understands guitar pickups at all.  It is all verbal smoke and mirrors.

Yep. It's not actually AI. It's just a language learning model that repeats what it's been fed. At some point, it picked this info up somewhere and now it just appears to be regurgitating whatever it "learned", whether right or wrong. The biggest issue here is that these things don't know when they're repeating nonsense. So no matter what they say, iys presented as fact.

[woundup]

I do have a question regarding the first post in the thread. What's an "exciter" and how does it work? I saw one on a vid on YouTube and I asked that guy but I don't think he replied.

Whats it for? I assume it's used to "excite" the pickup being tested? So it's used to induce the voltage into the pickup, essentially replacing guitar strings and strumming/plucking a note? Is that close?

[ms]

Feb 16, 2024 3:07:11 GMT -5 woundup said:

I do have a question regarding the first post in the thread. What's an "exciter" and how does it work? I saw one on a vid on YouTube and I asked that guy but I don't think he replied.

Whats it for? I assume it's used to "excite" the pickup being tested? So it's used to induce the voltage into the pickup, essentially replacing guitar strings and strumming/plucking a note? Is that close?

It's a coil, with or without a magnetic core, a ferromagnetic permeable material.  A permanent field is not needed. An audio current passing through the coil wire causes a time varying magnetic field.  When placed so that the field passes through the pickup coil, the voltage induced in the pickup can be used to characterize its performance.  The pickup has inductance, resistance and capacitance, and so the analysis yields information about these components.  It also gives information about losses caused by currents in metal parts.  These currents affect the electrical component values and also can reduce the output of the pickup by canceling part of the exciting field.  If instead you apply a voltage to the pickup terminals and measure the current through it, you get the impedance as a function of frequency, which is also a measure of the electrical components.  Both kinds of measurements are necessary for a complete characterization of the pickup, but such a complete measurement could be more than you need.