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Individual Piezo Transducers


alloyguitar
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Long story short, I'm needing to wire the signal from every string on the instrument to a seperate output...all tied together via a usb cable.

Where I'm getting hung is the whole "separate signal" thing. Easiest thing I can figure out is to use piezo elements similar to a fishman bridge. My question is: if I somehow manage to isolate each signal from one another, what would I need other than the piezo elements? I'm thinking that I shouldn't need a preamp, as I can balance the signal via software on my computer, so that leaves me with the elements themselves, wire and solder and all the usual wiring stuff, and the circuitry to interface via usb?

Just checking my footsteps, am I missing anything?

Any help/input/better ways to accomplish this would be greatly appreciated.

-Devon Goodspeed

P.S. The reasons for all of this being that we're developing software as an instruction on how to play guitar, since I'm sure that someone was going to ask.

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Long story short, I'm needing to wire the signal from every string on the instrument to a seperate output...all tied together via a usb cable.

Where I'm getting hung is the whole "separate signal" thing. Easiest thing I can figure out is to use piezo elements similar to a fishman bridge. My question is: if I somehow manage to isolate each signal from one another, what would I need other than the piezo elements? I'm thinking that I shouldn't need a preamp, as I can balance the signal via software on my computer, so that leaves me with the elements themselves, wire and solder and all the usual wiring stuff, and the circuitry to interface via usb?

Just checking my footsteps, am I missing anything?

Any help/input/better ways to accomplish this would be greatly appreciated.

-Devon Goodspeed

P.S. The reasons for all of this being that we're developing software as an instruction on how to play guitar, since I'm sure that someone was going to ask.

I'm not very clear on what you're looking for, so let me see if I have this right. You want to have six separate channels of audio, one for each string, coming into the computer via USB. Right so far? This is a complicated project. You can't just send audio over a USB cable. You will need to digitize it. This is not quite as simple as it sounds. Say you were going to build a circuit to allow you to do this.

At a minimum, your circuit would need:

A/D converters to digitize the incoming audio from each string.

A microcontroller to construct packets, do general bookkeeping, setup I/O, and whatever other stuff you'll find you need.

A chip to allow the microcontroller to talk to the computer over the USB link. This isn't strictly a necessity, but it's much easier than actually rolling your own USB interface.

Plus all the "glue" to get the chips to talk to each other, some sort of power supply, maybe external clocks and/or memory depending on what sort of microcontroller and A/D you use.

This would require a multi-layer PC board, and most of the parts will be small surface mount types. If you don't feel up to doing the layout (I sure wouldn't!), there are companies that will do the layout for you. It will cost, though. Getting the board fabbed won't be hard, but it could be costly, especially in small runs. If you can't solder SMT, then there are people that can do it for you. Again, it won't be cheap. You still need to be able to draw up the schematic, write the embedded code, and troubleshoot the device when you find out the first prototype doesn't work right. Drawing the schematic isn't quite as simple as it sounds, either. There are a number of ways to attack this problem, and some trade-offs involved in each way. You need a firm understanding of mixed-signal circuit design and embedded programming to make this work.

I'm not trying to burst your bubble or anything, but you don't sound ready for a project like this. This would be a good-sized undertaking, even for a hardcore electronics DIY'er. It requires skills in a number of areas, specialized equipment and software, and time and patience. Maybe there is some sort of multi-channel USB sound card out there that you can use instead? If we were to build something like this at work, there would be at least three engineers on it, plus techs and stuff. That's just for the hardware. You still need to write computer-side software for this stuff, too.

Well, I don't know if this answers your question or not, but at least it's something to think about.

Edited by fookgub
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Well I understand the whole "digitizing the signal" thing, which would be my brother's area of expertise. Honestly, I don't really have a damn clue about circuit boards, or anything of that sort. I'm just trying to get the analog side of this figured out, and let him figure out how to get it to interface with the computer and whatnot.

But yes, you do have the general idea correct. I need six seperate signals, one for each string.

Any thoughts on how to design a pickup system of this sort?

I'm trying to stay away from having to wind my own pickups, and I'm afraid that there would be too much interference, which is why I was leaning more towards piezo.

-Devon Goodspeed

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I believe most Fishman bridges will sum to a mono signal before output.

To be honest, I'm mainly going to echo (less effectively, I think!) what fookgub has already said: Most of the project is seemingly not fully planned out-- you may indeed have a brother that's a wiz, but I would wait until he's confirmed that he's able to make all the stuff fookgub has already described. It's non-trivial to the extreme. It's not going to be worth your time making the thing if the interface isn't in place, but really, it's the interface that's going to be the astonishingly difficult part compared to the hexaphonic piezo pickup.

What's your intended end-goal? That's the question that needs to be answered before any of us can even speculate properly. But since I enjoy blind speculation, I'll add to fookgub's post-->

There seem to me that there are 2 broad alternative approaches if it turns out that your brother isn't able to design an interface, both of which require outlay of cash:

1. Look into the Graphtec Ghost system. It uses Hex piezo elements, and can be sent to a synth module; I'm sure you could bake up your own application for it, if you're highly technical; but the actual hardware design is at least half-complete with such a system.

2. Instead of designing an interface, just look at the cable as a carrier for your signal(s). I would choose a different cable type other than USB... maybe a network cable? There are 8 conductors, but just don't use one of'em. Then buy a multi-input audio card. The network cable (or whatever other multi-conductor cable you use) is just a bridge. At one end is your hex pickup, and at the other end is a box with 6 standard audio cables coming out. These get plugged into your multi-in audio card.

I suspect option #2 is the one that would work best for you-- you DO actually need preamps with a piezo signal (even if they're going into the computer), and the multi-in soundcard can potentially provide this. You could even add in the saddles from option #1 and most of the work is then done for you.

But, back to the real question:

What is your intended end goal? Ie. how will this tool aid your software plan?

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As simply put as I could possibly make it, the program is being designed to tell which note(s) you are playing, and on what strings they are being played...So, in theory, tab could be displayed on your computer's monitor, and it could grade you on your performance. I.E. it would tell you if, and where, you messed up.

...also, it could be used as a way to tab something in realtime, instead of writing it down on little pieces of paper that will only get lost or thrown away.

I know the whole concept sounds awfully complicated, and I may look into using a cat-5 cable as the means of transferring the signal from the guitar to the computer. As of this moment, no actual funds have been invested in the project, we're just trying to see if it would be possible to do with piezo's, and how difficult such a contraption would be. I'm thinking of something attached to the front of a TOM bridge, that would be able to pick up the signal from the strings in a location that it would not be possible to be damaged by the actual string movement.

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Sorry about that earlier post. Sometimes I just tend to grab an idea and start running with it. If you want to start experimenting with this idea now, you should probably forget about USB and all the stuff I said above. Here is my suggestion:

Individual piezo transducers are the way to go, and I think Greg's suggestion of looking into the Graphtech line is a good start. Each transducer will need its own preamp. Google "Tillman preamp," and the first hit will be a nice little single FET preamp that works pretty well. Simple enough that you should be able to build one for each string. Note that all the preamps can share the same battery (and by association, the same ground), but everything else should be separate.

Once you've got the saddles installed and the preamps built and working, you need to get the sound into the computer. I'll leave you to your own devices on a cable, except to suggest that you should buy something that's shielded and meant for audio. There are a number of DIN style connectors that would be worth checking out, because your guitar should have some sort of jack on it (verses just pigtailing the cable). Mouser and Digi-Key are the best places to start looking for this kind of stuff, at least in the US.

To actually get the sound into the computer, where you can do something with it, I recommend you start with an off-the-shelf solution. Finding a sound card with 6 inputs might be tough, but I think the M-Audio Delta 1010LT will fit the bill. You will want to check this out first, though. If it was my project, I would terminate my cable with a DIN connector into a breakout box that has all the leads necessary for hooking up to the sound card.

Anyway, I don't know if that will tell you anything you didn't already know. Getting this to work from a hardware perspective shouldn't be too difficult, but there are many finer points that you will have to learn along the way. I can't help you much with the programming side, as I've never worked with either AISO or DirectSound before, but this should at least get you started with sound coming into the computer.

Edited by fookgub
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Just to add to that post, there are tonnes of multi-in audio cards; the trick is finding one that's not cost-prohibitive. :D

I think the next most important thing to look at after proof-of-concept is going to be: how do you distribute this to the would-be student at a price that makes them want to buy the package? What's the Roland guitar-synth/MIDI pickup like? If you can interface with that, it'd give you a solution to deliver to people who already own that pickup. And if they don't already own it, it can be easily installed without modification to the guitar.

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Off-the-shelf, the Ghost saddles with their Hexpander MIDI preamp will do the A/D conversion for you (may or may not require the Acoustiphonic preamp as well....not sure, but their tech department is very good).

For guitar-computer interface, the Ghost system is compatible with Axon's MIDI guitar controller, which (they claim) somehow has the ability to discern which string you're playing as well as the note. If that's true, then all you need to do is code your software to take the output from the Axon and do with it what you want. The Axon is the only MIDI controller that claims to know which string you're playing...that I'm aware of.

I'd try this with a single saddle first...though that's not where you'll spend the big bucks if you go this route.

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I wonder how on earth it could know which string you're playing on? Maybe there are slight frequency differences between a note played on the low E string and the A. Either way, I would think that being off on your tuning even by a little bit would throw that completly out of whack.

Weird.

-Devon Goodspeed

That's where the individual transducers come in. If there's one signal path for each string, it's down to the channel coming in rather than the pitch of the note.

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midi is done just like that. each string is picked up. you have 6 individual pickups. it knows which string is which.

That is how it can make bass on the 2 low strings, or any combo you can think up and your synth is capable of.

I have an older fishman bridge ona strat and it has a lead for each pickup (each string)

this will work

the ghost system does as well, if you just want the pickup I think it is 100-120 dollars.

it comes with a connector to sum the pickups. you just remove that.

the rest is up to your brother.

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  • 1 year later...
Well I understand the whole "digitizing the signal" thing, which would be my brother's area of expertise. Honestly, I don't really have a damn clue about circuit boards, or anything of that sort. I'm just trying to get the analog side of this figured out, and let him figure out how to get it to interface with the computer and whatnot.

But yes, you do have the general idea correct. I need six seperate signals, one for each string.

Any thoughts on how to design a pickup system of this sort?

I'm trying to stay away from having to wind my own pickups, and I'm afraid that there would be too much interference, which is why I was leaning more towards piezo.

-Devon Goodspeed

if you use seperate piezo film elements under the bridge hook each one to an op amp voltage follower. you can use a second op amp to add some gain if needed. pay attention to the impedences. there are cheap pic microcontrollers with built in a to d and usb support and a huge developer community on the web. As far as board layout try protel isis /aries. single sided boards are easy to etch at home, double sided are easy as well, as long as you avoid plated through holes, you have to solder both the top and bottom of the board. Don't cheap out on the op amps and use something like a 741, go with burr brown opa627 if you can afford them. the opa 134 series is not bad as well and a lot cheaper

Amplexus

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As simply put as I could possibly make it, the program is being designed to tell which note(s) you are playing, and on what strings they are being played...So, in theory, tab could be displayed on your computer's monitor, and it could grade you on your performance. I.E. it would tell you if, and where, you messed up.

Hmmm...an interesting concept but I don't think it is a marketable "product"...too much dedicated hardware.

Basically a midi guitar is what is required and the ghost system may be able to do that...or one of the roland stick on hex things might be more useful.

As a software thing it could find a market perhaps bundled with synth pickups and such, but with the top end roland synths only getting dearer, perhaps the market is rediculously small for the work involved.

There is plenty of software that will accept a midi signal (from a midi guitar) and notate it...the "guitar Hero" kind of interface is a novelty though. The problem there from a performance thing is that most tab is suspect and none of it correctly timed as per a performance. That is, a guitar solo will not accurately reflect the timing of notes and real time "scoring" will be all but impossible due to inevitable delays in the A/D conversion...ie tracking...potentailly it could make your playing worse!

Anyway...I did have a bit of experience with trying to build my own hex piezo type things with not much success. I cut up piezo elements to fit under the strat saddles...but with these things there are vibrations in the bridge itself from all the strings so there tends to be some bleed through regardless...mainly though, it is virtually impossible to hand solder all those wires to tiny homemade piezo crystals....in fact, cutting the element almost always results in the loss of most of the crystal layer...very frustrating.

But...a lot depends on the preamps which will be necessary...extensive filtering is probably require to get rid of all that harmonic rich artifacts before heading off to the A/D and midi thing.

I found out last year that a lot of the early synth hex pickups were actually made from tape heads...so this might be something to experiement with...you will still need preamping. Basically, six little tape heads, perhaps from old cassette players right in front of the bridge like the roland GK-?? thing...but realistically, you could probably find and ebay GK thingy that could surface mount to most guitars and produce the required signal to start you off on the software side of things.

I fear though that the tracking issues will undermine the whole scheme, and the quality of notation and such is very suspect as it is, so potentially you could learn to play as written, but not sound anything like a "performance" which could be a bad thing as a learning tool.

As a side note...at uni many years ago someone developed a program to notate recorded solos and did some jazz stuff...the reality of an effective performance is that the notes are easily transcribed but the timing is insanely complex in real music. So, along with the aversion guitarists universally have for notation as a rule, makes the project a little dubious from a practical point of view.

I have played with guitar pro of late for notating things myself...it will accept midi files and notate, tab and display on a fretboard...maybe a good thing to check out as a stand point or some way of adding your ideas to it perhaps.

good luck

pete

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