Ibanez "Twin Peaks" wah pedal: Two resonant frequencies

[foxmilder]

Ibanez are currently advertising a dual-inductor wah pedal: the "Twin Peaks", aka TWP10.

It's sufficiently complex as to make the product page a little confusing on the first reading, but it's an interesting idea. The basic elements are as follows:

1. A single expression pedal controls the sweep of two resonant filters
2. A "balance" control adjusts the relative "peak levels" (I have no idea whether it's blending the volume of two signals, adjusting the resonance of two filters, or some other mechanism)
3. A "tone" switch selects between two "tone modes": "high" and "low". This is needlessly confusing in its phrasing, but this switch adjusts the sweepable range of both resonant filters; it doesn't appear possible to adjust the range of each filter separately.

 If nothing else, users like antigua may find it amusing to encounter a rare case of actually-existing "dual resonance"!

[foxmilder]

Personally, I'm not a particular keen user of wah pedals. I'm more interested in the tone-shaping capabilities of dual resonant peaks. Some of the more unique "voices" of the Fishman Fluence range involve frequency responses characterised by two resonant peaks. I'm curious as to the extent to which such sounds are of interest and/or practical utility to guitarists. That is to say: I wonder whether tone-shaping tools of this nature produce tones we would subjectively enjoy.

[kitwn]

Feb 8, 2024 1:19:50 GMT -5 foxmilder said:

Personally, I'm not a particular keen user of wah pedals. I'm more interested in the tone-shaping capabilities of dual resonant peaks. Some of the more unique "voices" of the Fishman Fluence range involve frequency responses characterised by two resonant peaks. I'm curious as to the extent to which such sounds are of interest and/or practical utility to guitarists. That is to say: I wonder whether tone-shaping tools of this nature produce tones we would subjectively enjoy.

I've studied the Fishman patent and am interested by their method of adding a serious amount of digital signal processing right inside the pickup. Do you have any links describing the two-resonant-peaks responses and samples of the resulting sound?

Kit

[foxmilder]

I haven't personally investigated this in a remotely scientific way, but others users have shared bode plots of the "Open Core Classic" set, and of the "Modern Humbucker Ceramic" pickup, the de-facto bridge pickup of the "Modern" set.

In the linked thread about the Classic set, there's some discussion of, and excerpts from, an exchange between the OP and a member of the Fishman R&D team. With regarding to (I think) the neck pickup, he suggests the bode plots misrepresent the magnitude of the lower peak, and the slope of the higher peak's rolloff (represented on the plot as a second-order LPF). The former objection I cannot judge, but I find the latter claim dubious.

As to what they sound like: I have the exact "Open Core Classic" set that is the subject of that discussion, but they're not currently in a guitar. When I did have them in a guitar, I felt they did a very good impression of a standard PAF with voice 1, and passable single-coil sounds with voice 3. Voice 2 on the bridge pickup is meant to sound like a high-gain passive humbucker, which I have no use for; I didn't try it. Voice 2 on the neck pickup is one of the dual-peak sounds: the specs locate the two peaks at 350 Hz and 4.5 kHz. I didn't like it, and can't remember much more than that.

I don't have time to take pictures and write it out now, but I also have a set of their "single-width" pickups for Strat, which use quite an interesting design. Only the bridge pickup contains a preamp, but the signal is sent to the preamp *after* the pickup switching is done. The middle and neck pickups are purely passive; the bridge pickup appears to be the same, only it's packaged alongside the preamp under a piece of plastic. The pickups are wired to the 5-way switch, the 5-way switch is wired to the preamp input, and the preamp output is wired to the volume pot. This, I suspect, is at least partly intended to produce the characteristic features of the parallel bridge & middle and middle & neck pickup combinations in the passive domain, but I may be wrong about that.

In any case, I'd like to try document it for users here, because as far as I can tell, you could theoretically wire *any* guitar pickup into that preamp system. Even with a standard SSS layout, the possibilities are far greater than with most active pickups — I think. Here's the legend for the absurd number of leads coming out of the bridge pickup & preamp assembly. I'll take some pictures of my set when I have the time.

[kitwn]

Some interesting details in those linked threads.

It's interesting that in spite of all the prejudice against transistors and digital audio I've read over the years, plus claims from the genuine-1950's-orange-blob-capacitors-sound-better brigade nobody seems to be suggesting that taking the output of a pickup coil through an IC buffer amp, an analogue/digital converter, digital signal processing, a digital/analogue converter and another IC buffer amp all inside the pickup case makes the resulting sound irreversibly crap.

Kit

[foxmilder]

Are we sure the Fluence pickups actually are using DSP to produce their desired frequency response?

In one of the threads on this forum — I'm not sure which, unfortunately — there's a discussion about the Fluence design approach between antigua and Frank Falbo, who apparently designed the pickups. To put it bluntly, Falbo ends up saying what he always does: there's a magic ingredient, but it's a trade secret.

I don't know enough about electronics to make any big claims, but to my eyes, the bode plots of the Fluence pickups' frequency response look a lot like the transfer function of a Pultec-style EQ unit, which is a passive EQ followed by an active gain-stage. Imagine starting with a ruler-flat frequency response, then adjusting it with these controls:

[foxmilder]

Feb 13, 2024 16:31:31 GMT -5 kitwn said:

It's interesting that in spite of all the prejudice against transistors and digital audio I've read over the years, plus claims from the genuine-1950's-orange-blob-capacitors-sound-better brigade nobody seems to be suggesting that taking the output of a pickup coil through an IC buffer amp, an analogue/digital converter, digital signal processing, a digital/analogue converter and another IC buffer amp all inside the pickup case makes the resulting sound irreversibly crap.

It's funny when the worlds of traditionalist guitarists and traditionalist audio engineers happen to intersect, because their beliefs are identical in form, but wildly divergent in content. The adjectives guitarists use to describe the mythical properties of tube amplifiers, for example — "warm", "round", "smooth", "rich", "creamy" — are often used by audio engineers to describe legendary solid-state preamplifiers!

[sumgai]

kitwn



I learned a long time ago that if some given person opines that such-and-such is the bee's knees, then I ask just one question of them - "Will you sit down for a double blind test?". Invariably, I get "No" for an answer, accompanied by a variety of reasons excuses. At that point in time, I dismiss them from my world view, and continue on my way.

Opinions are one thing, facts are quite another. If a person doesn't trust his own statements enough to be tested for veracity, then I have to conclude that it's ego talking, in the form of confirmation bias. (And that's the clean version of how I wanted to describe it!)






sumgai

[foxmilder]

sumgai,

Your may already be aware of this, but there's a well-known, largely respected user on a very popular audio engineering forum who believes that double-blind A/B trials, by putting pressure on participants, cause them to second-guess their judgment. This, he argues, means they are only able to make use of their "work ears" when their ability isn't being tested.

This particular guy actually did participate in a double-blind trial, in which he confidently and authoritatively answered all the experimenters' questions. It was only after seeing the results that he decided to rewrite the laws of physics.

The thing I find most telling about these guys is the slow realisation, dawning upon me only when I see a picture of them, that the people claiming to be able to hear artefacts at 20 kHz are twice my age, and have spent half their lives listening to extremely loud sounds.

[sumgai]

foxmilder .


Yeah, I used to get that more often that seems reasonable - "Sorry, I'm no good at tests, too much pressure", and similar excuses. The other one is "How do you know that I'm not cheating, if we're so far apart?", to which I would reply "If you show up on my doorstep, I'll pay your way here and back regardless of the results. But you have to put your money where your mouth is first, and pay your way here as a matter of trust in your own statements".

Never got a taker, not once in more than 40 years.

Why so long? 'Cause I'm deep into my 70's and I know for a fact that my hearing was damaged beyond all repair in my youth. Never mind loud music, never mind racing (drag, Formula Vee, stock cars, hydroplanes, etc.), try sleeping less than 100 feet from a pair of 155mm howitzers, when at 1:30 in the morning they decide to start shelling a Viet Cong stronghold. That'll fix your hearing right smartly, take my word for it.

So for me, call it a perverse form of confirmation bias if you wish, but no, I don't believe in Golden Ears. If someone truly has them, then they've lived a very sheltered life, and probably not one that I'd've liked to live.

Now let me dodder off back to my morning cup of tea.  My chronic lumbago is acting up, don't you know....






sumgai

p.s. Yeah, I know, my profile says I was born on Jan 1st of 1980.  For those who don't know, the joke goes like this: The IBM PC was released to the public on August 12th, 1981.  That machine could "back date" only to 1/1/1980 - any further, and the thing would fold up like a tent in a desert storm.... sort of like dividing by zero, you never knew how it was going to react.  But that's where my "birthdate" comes from.

And no, for quite obvious reasons, I'm not really located in the Vatican, that's also a joke - I'm about as far from religious in the Catholic vein as it's possible to get.  (But I'm not quite the Anti-Christ that they're so afraid of. )

[kitwn]

Feb 19, 2024 20:30:11 GMT -5 foxmilder said:

Are we sure the Fluence pickups actually are using DSP to produce their desired frequency response?

I can't answer that with a definitive 'yes', but if you'd like to Google 'US Patent 9,355,630' and then come back here I'll explain my reasoning...

In amongst the standard patent legalese is a description of a low-inductance (i.e. wide-bandwidth) coil followed by an active filter, which can be analogue or digital, to provide the individual voice of the pickup. More than one filter can be included to give multiple voices to a single pickup. A key point of the patent is that all this machinery is inside the standard size pickup case, so you can't copy the idea.

In the patent, Figure 1C shows an embodiment of the invention with two voices selected by a switch. Could be analogue or digital.

Figure 2 shows an option with an unlimited number of filters which can be programmed by an external computer. This is more fully described in the text and has to be digital.

Implementing multiple filters inside the pickup case is going to be far easier to do in DSP than installing multiple analogue circuits and the technology is now well established. Fishman have been keep to promote their pickups with a third voice and I'd say this is how they've made that practical and cost-effective.

When you think about how easily this technology lends itself to making a whole range of 'bespoke' signature pickup sets it's a no-brainer if you've already committed yourself to a business model based on convincing guitarists to buy pickups with silicon on the inside.

Kit

[foxmilder]

First of all: thankyou, kitwn, for directing me towards that patent, which I would never have thought to dig up on my own. I'm currently meant to be focusing on my University studies, so I should probably avoid disappearing down that rabbit-hole for now (especially given my meagre grasp of the relevant scientific and mathematical concepts). But I will make a note of it, and when I have enough free time, I'll look it up and fail to understand it in greater detail.

I'm glad you reminded me about this discussion, which I had intended to return to, then completely forgotten about (you may notice a theme emerging here). Just a few days ago, while searching for something else, I happened to pick up the bridge pickup from my Fluence "single-width" set. As I may have mentioned earlier, I don't have the testing equipment to contribute to the forum's "pickup testing and modelling" research program, so I am ordinarily unable to offer any particularly meaningful new information or technical findings regarding the properties of electric guitar pickups. But it occured to me, holding that strange 7-conductor pickup/preamp assembly, that the design of this particular pickup set, in which the preamp is located after the 5-way pickup selector, presents an unusual opportunity for technical measurement — I think.

Let me know if this makes sense:

1. Because the signal enters the preamp via an input lead, and exits via the output lead, we can measure the frequency response of the preamp independently from that of the pickups.
2. Because we aren't measuring the pickups themselves, we don't need to manipulate the string/pickup interface to take a measurement.
3. If I'm not mistaken, we could directly measure the frequency response of the preamp by connecting an audio signal chain to the input and output leads, running a pulse or sweep through this signal chain, and creating an impulse response representing the transfer function of the preamp.

If this is possible, this is a methodology I do have the tools to carry out (I think).

Is it possible?

[kitwn]

Mar 6, 2024 22:57:17 GMT -5 foxmilder said:

First of all: thankyou, kitwn, for directing me towards that patent, which I would never have thought to dig up on my own. I'm currently meant to be focusing on my University studies, so I should probably avoid disappearing down that rabbit-hole for now (especially given my meagre grasp of the relevant scientific and mathematical concepts). But I will make a note of it, and when I have enough free time, I'll look it up and fail to understand it in greater detail.

I'm glad you reminded me about this discussion, which I had intended to return to, then completely forgotten about (you may notice a theme emerging here). Just a few days ago, while searching for something else, I happened to pick up the bridge pickup from my Fluence "single-width" set. As I may have mentioned earlier, I don't have the testing equipment to contribute to the forum's "pickup testing and modelling" research program, so I am ordinarily unable to offer any particularly meaningful new information or technical findings regarding the properties of electric guitar pickups. But it occured to me, holding that strange 7-conductor pickup/preamp assembly, that the design of this particular pickup set, in which the preamp is located after the 5-way pickup selector, presents an unusual opportunity for technical measurement — I think.

Let me know if this makes sense:

1. Because the signal enters the preamp via an input lead, and exits via the output lead, we can measure the frequency response of the preamp independently from that of the pickups.
2. Because we aren't measuring the pickups themselves, we don't need to manipulate the string/pickup interface to take a measurement.
3. If I'm not mistaken, we could directly measure the frequency response of the preamp by connecting an audio signal chain to the input and output leads, running a pulse or sweep through this signal chain, and creating an impulse response representing the transfer function of the preamp.

If this is possible, this is a methodology I do have the tools to carry out (I think).

Is it possible?

1) DON'T get distracted from the principle subject right now!!!! What are you studying, if that's not a rude question?

2) Patents are a really good way of finding out about a particular manufacturer's pickups and plenty (especially US patents) are easily available from Google if you can find the numbers to plug in. The patent must, by definition, tell you more than the company may want to reveal on their websites. Fishman give very little away in the body of their site but kindly have a whole page dedicated to listing their patent numbers! It's linked at the foot of the home page.

Once you have one patent it will refer to other, previous ones from other people and so the chase goes on. I even found one (for Leo Fender's last pickup designs for G&L) by pausing a video on their website. The patent number is stamped on a coil former. What you actually discover is that there is very little real innovation and many designs are just an aim to get round someone else's existing patent. It's amazing how little novelty is actually required to get a new patent. Think of every minor variation of how to wrap some wire round a magnet and somebody has patented it and then got their marketing department to hype the s**t out of it until it's the next best thing since soft toilet paper.

3) You can measure the frequency response of any component/system if you have access to it's input and output and the appropriate interface for each end. A pre-amp alone should be completely flat (though it may have gain), though it's influence on the impedances seen at each end may affect the overall response of the rest of the system it's a part of. Increasing the self-resonant frequency of a pickup connected to it's high-impedance input, and/or reducing high-frequency loss in a long cable connected to it's low-impedance output being the key reasons for putting pre-amps into guitars.

4) I'm going to steal this quote from you... "and when I have enough free time, I'll look it up and fail to understand it in greater detail."

Kit