Guitar Selection Help (University Project)

Henlein

Hey everybody, I'll try and keep this as short as possible ?

I'm a final year electronic engineering student at Tuks with my project being a guitar modelling system (kind of like the Line 6 Variax and Fender VG systems where one guitar's timbre is modified to that of another such as making a Les Paul sound like a Strat etc.).

I am planning on doing this using a digital signal processor and a magnetic hexaphonic pickup (one output per string) (from http://www.ubertar.com/hexaphonic/ for those who are interested) where I will normalise the frequency spectrum of the guitar the system is installed into before multiplying it with the desired spectrum of a well known guitar design.

Unfortunately, some of the specifications I have set out include that the system (consisting of the pickup and a stomp box) must not require permanent modifications to the guitar its installed in and it must cost less than R5000 to produce. This is where the problem comes in:

-I would preferably want to use the single coil hexaphonic pickup as it is almost half the price as the humbucker ($135 versus $235) and I would rather be conservative and save budget for more processing power if it is needed

-I want the guitar to have as much sustain as possible because it will be easier to 'remove' sustain rather than 'add' (amplifying the dying signal will result in a noisy output that will lessen my measures of performance)

-Ideally the single coil should be as close to the bridge as possible where the strings move less, resulting in less cross-talk between the string channels (Its not a massive problem if its not but this will just result in better modelling results)

-budget-wise the guitar doesn't count as part of the system and hence its price isn't so important but I am a student... So lower the cost the better with a maximum cost of lets say R5000 (I can go higher but would rather not)

I tried looking at second hand guitars with a set neck and single coils but there is nothing that I could find... Even checking the new models of the major manufacturers turned up very few answers... What do you guys suggest?

Also regarding the project itself I would rather not discuss it at this stage as the University might have an issue with that. I'll post results and more information for those of you who are interested after everything is completed (probably December)

Thanks ?

AlanRatcliffe

You can pick up a Roland GK-3 on Ebay for R1500 - R2K. It's humbucking, but has a narrow string sensing window, so you retain your high frequencies (invaluable when modelling guitars like acoustics, Strats, Danelectros and the like). Mounted closer to the bridge than anything else too. Also, making your modelling unit 13-pin capable will make it cheaper (the hex preamps are built into the hex pickup unit) and more marketable (you can sell it to those who have magnetic or piezo hex-equipped guitars already).

Don't worry too much about sustain - any decent guitar will have more than enough to work with. Sustain is overrated and few players are playing notes that sustain longer than even a double-locking floating trem guitar can produce (especially at volume). Neck joints have far less influence on sustain than is popularly believed and far, far less than the bridge type. BTW - a Tele makes a great hex platform...

Gearhead

Why not take a Resomax bridge instead of a magnetic pup? It will give you guaranteed good results since it's been developed with both acoustic tone and good MIDI tracking as goals. It installs easily into any TOM bridged guitar and the modification is reversible so you could even borrow an instrument.

Heath

And maybe look at Perspex bodies they don't react like wood does

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Henlein

Thanks for the responses.

Alan, what is the exact reasoning behind the GK-3 retaining the high frequency range better? Also regarding the sustain, I was just thinking in terms of singe note mathematical correlation between the modelled output and the guitar I am modelling (unfortunately I need to conform to quantitative performance analysis), but I suppose I could always just focus on the correlation of the first part of the note with the reasoning that the sustain is not necessarily important most of the time. Lastly, why do you say a Tele is a good hex platform?

Gearhead, that resomax bridge does look like a nice option for both installation as well as results.

Tailon, I have specified that the system should work with any guitar so something very different to normal might be pushing things a little bit (I was just looking for something that would give better results- like testing a satellite system on a nice sunny day for best results)

With regard to piezo and magnetic options in general, I was planning on using a magnetic pickup as it would give more accurate electric tone in terms of dynamics and noise components etc. thus requiring less modification of the signal (I am modelling 3 electrics vs. one acoustic for now). Whilst in terms of the acoustic modelling I was focusing more on looking into the resonances of the body as well as the volume 'beats' etc. to simulate acoustic tone but I will definitely look into the piezo option though (maybe I could include both if I keep processing costs down?). What piezo systems do you recommend I look at? I can always build my own pre-amps if they are pricey (I can't imagine they are too hard).

Gearhead

If you are after body response modelling instead of pickup response modelling, it should not matter what pickup you are using as long as it registers a relatively broad spectrum. If you are after pickup response modelling, you should use all pickup setups available on the same instrument. It's as simple as that.
In general in research you will spend a lot of time in the beginning talking nonsense until you figure out exactly what it is you want to do. My advice would be to do a thorough lit review to figure out what has been done before (a lot) and what others recommend should still be done. Nothing like a research proposal that cites recent literature saying that this should be done.
How would your DSP approach differ from, say, a Kemper profiling amp or a Fishman Aura preamp?

AlanRatcliffe

Henlein wrote: Alan, what is the exact reasoning behind the GK-3 retaining the high frequency range better?

While it is a humbucker, the much narrower string sensing window means that phase cancellations are in a much higher frequency range than you will find in a hex pickup designed in a normal humbucker size package. Also the coils are very low Z compared to a normal humbucker, so the resonant frequency is far higher.

Also regarding the sustain, I was just thinking in terms of singe note mathematical correlation between the modelled output and the guitar I am modelling (unfortunately I need to conform to quantitative performance analysis)

The thing is that most guitars have more than enough sustain to mimic each other in a playing situation - whether notes sustain for 6 seconds or 60 is irrelevant when normal playing mutes or retriggers notes in one or two (usually less).

I suppose I could always just focus on the correlation of the first part of the note with the reasoning that the sustain is not necessarily important most of the time.

From everything I've read, the attack is far more important in identifying a sound. That was the whole basis of LA synthesis in the '80s, which used PCM sampling for the attack and conventional synthesis methods for the DSR (before sampling synths became the norm for realistic sounds).

Lastly, why do you say a Tele is a good hex platform?

Experience. ? I've had Hex pups in/on virtually every type of guitar over the last 25 years.

Gearhead, that resomax bridge does look like a nice option for both installation as well as results.

Graph Tech are by far and away the best system and the only brand I now use in my (electric and nylon) guitars (I even helped them beta test a few hex products a few years ago). You can also go for their GHOST saddles for many types of guitars, which are far cheaper than buying the whole Ghost equipped bridge. Their Hex preamp is fairly expensive though (but its more than just six preamps...).

With regard to piezo and magnetic options in general, I was planning on using a magnetic pickup as it would give more accurate electric tone in terms of dynamics and noise components etc. thus requiring less modification of the signal

Good point. I use my hex nylon a lot, so I know it can be done, but Roland uses mostly EQ to compensate for different pickup systems and sources, so the acoustic tones do sound better from piezo guitars and electric tones from magnetics like a GK-3.

Henlein

Gearhead wrote: If you are after body response modelling instead of pickup response modelling, it should not matter what pickup you are using as long as it registers a relatively broad spectrum. If you are after pickup response modelling, you should use all pickup setups available on the same instrument. It's as simple as that.

I'm modelling the combination of both the body and the pickups (the complete sound of the guitar) so yes basically all I need is a pickup that registers a broad spectrum, but the dynamics (from what I have read the piezo is very non linear) and the inherent noise of the pickup does make a difference when it comes to the mathematical correlation (which is my primary goal specification) as well as the overall 'naturalness' of the sound.

Gearhead wrote: In general in research you will spend a lot of time in the beginning talking nonsense until you figure out exactly what it is you want to do. My advice would be to do a thorough lit review to figure out what has been done before (a lot) and what others recommend should still be done. Nothing like a research proposal that cites recent literature saying that this should be done.
How would your DSP approach differ from, say, a Kemper profiling amp or a Fishman Aura preamp?

I am still in the process of reviewing the relevant literature as I have been so busy with my multitudes of assignments and up-coming tests. However, most of the literature I have found thus far is more concerned with synthesis than modifying the spectrum of an input and its hard to find literature on the specific technical side of the commercial products unfortunately.

Alan Ratcliffe wrote: From everything I've read, the attack is far more important in identifying a sound.

From what I have read, this is true. However, it does come back to the fact that a mathematical correlation between signals will not really discriminate between the attack and the sustain unless I include some sort of weighting factor (which I could well do).

With regard to a Tele being a good platform: That suits me since i don't have one and any excuse is a good one to expand one's collection ?

By the looks of it, the Graph Tech hex pre-amp is solely for the purpose of converting to MIDI rather than being a regular hex output (It would be a bit too expensive use anyway though). Also it appears that the Acousti-phonic pre-amp has some sort of processing built in so it would probably be beneficial to just make my own.

Where would be the best place to get hold of the ghost saddles? From the Graph Tech website? Also am I correct in understanding that using these saddles require a hole to be drilled into the bridge for the output wires? (How else would you do it I suppose?)

Finally, am I correct in understanding that a single coil pickup will retain the higher frequency components better than a humbucker? I am assuming this due to the sound of single coil equipped guitars having a stronger high end, the coil having a lower impedance and a narrower string sensing window (as you mentioned for the GK-3?).

AlanRatcliffe

Henlein wrote: With regard to a Tele being a good platform: That suits me since i don't have one and any excuse is a good one to expand one's collection ?

Natch! ?

By the looks of it, the Graph Tech hex pre-amp is solely for the purpose of converting to MIDI rather than being a regular hex output

Nope, there is no conversion at all. It preamps the individual channels (and brings down the Z to something more suitable for driving through a longish cable), applies a sub frequency high-pass filter (very low frequencies cause problems with various modelling and pitch-MIDI units). It also adds in the switches and pot to the 13-pin output for the modelling/synth unit to use.

Also it appears that the Acousti-phonic pre-amp has some sort of processing built in so it would probably be beneficial to just make my own.

I'm not sure how much processing is in there aside from the mid boost circuit (which I usually ignore). The saddles sound remarkably good by themselves Fortunately, for hex, you don't need the acoustaphonic pre anyway...

Where would be the best place to get hold of the ghost saddles? From the Graph Tech website?

Marshall Cape are the local distributors, but I'm not sure what stock they hold as I still buy direct (and haven't needed anything for the last few years anyway). Their website works well and obviously has the full range, but you can often find some of their products from other US online suppliers at slightly better prices.

Also am I correct in understanding that using these saddles require a hole to be drilled into the bridge for the output wires? (How else would you do it I suppose?)

Ideally yes - that's how I and most pro installers fit them, but the manual suggests running them over the surface of the bridge and under the pickguard (F-style top route guitars) or under the bridge pickup's mounting ring (G-style rear- rout).

Finally, am I correct in understanding that a single coil pickup will retain the higher frequency components better than a humbucker?

Yes. But don't forget that with hex pups you are working with much smaller/lower Z coils than conventional magnetic pickups anyway, so a lot of the things that subdue the high end in a full-size HB fall away: the resonant peak moves up to ranges that you can ignore; if you have a narrower string sensing window (as in the GKs), the two coils sense almost identical parts of the string, so there is minimal time shift and phase cancellation in the audible range.

Coming back to the piezo v magnetic discussion. I would think that the faster attack of the piezo would be a better base to work with as I imagine it's easier to slow a fast attack than speed up a slow one (at least without introducing a slight delay)...

Gearhead

So we all agree that you need a GK-3 (I am happy to borrow you mine for the duration of the research), a set of Tele Ghost saddles and six buffer amps? ?

Henlein

Alan Ratcliffe wrote: Coming back to the piezo v magnetic discussion. I would think that the faster attack of the piezo would be a better base to work with as I imagine it's easier to slow a fast attack than speed up a slow one (at least without introducing a slight delay)...

Yeah you are probably right, although there should probably be enough signal from the magnetic after a short delay to to work with.

Gearhead wrote: So we all agree that you need a GK-3 (I am happy to borrow you mine for the duration of the research), a set of Tele Ghost saddles and six buffer amps? ?

Yes, along with a Tele ? (which I now need to go about finding at a decent price) and if you could please lend me your Gk-3 that will be fantastic and make life much easier! Thanks! (I will probably only start needing it in June or so at the earliest as I doubt I'll get stuck into the implementation side of things until after exams)