Trying To Get That Pat Metheny Guitar Synth Sound - How To Do?

[Paul Marossy]

About 15 years ago I attempted to design something that would give me something similar to that Pat Metheny guitar synth sound (kind of like a horn). I originally tried to use an LM2917, etc and I tried revisiting the project a couple of weeks ago. I found some ways to make it respond better to all notes on the fret board but I just end up with something that is like a ring modulator.... which is NOT the sound I am after. 

Anyone have a vague idea of how Roland does it?

Original thread from 2003 is here: https://www.diystompboxes.com/smfforum/index.php?topic=11267.msg69185#msg69185

The sound I want to emulate (without tons of delay)

[garcho]

wow, that's one of the more singular guitar faces, forgot about his teeth

Do you want the function of the synth?

Or just that particular sound? Because if it's just the sound I think you could get really close by turning the guitar into a square/tri wave and then using a LPF to get that "soft focus" sound, then more distortion to add artificial "presence" to get some definition and articulation back. You would have way more sustain, and less fretboard/finger sound (read: less human, more synth). Maybe some CMOS stuff going into a gyrator going into more CMOS stuff? If you only want that sound I would say forget about tracking, gate/triggers, etc.

From that old thread, the legendary Tim Escobedo (emphasis is mine):

The F to V chip is a possibility. I think the real difficulty will be getting the VCO to scale correctly with the F to V chip output. In the synth world, pitches are usually scaled in 1V/octave, which makes interfacing easy, but requires sometimes very complicated circuitry to translate exponential scale to a otherwise linear VCO. And you'll probably have to drive the F to V chip with a comparator output anyway, as I think they usually want a clean square wave to track.

That's the CMOS square/tri thing. Assuming you only want one sound, the only thing that would be better about triggering a VCO with the guitar instead of just processing the guitar's signal would be infinite sustain. But if you get that, then you have the challenge of generating and sending an "off" signal with a guitar.

[Mark Hammer]

Didn't the "Trombetta" modification to the Jordan Bosstone do that?

[Paul Marossy]

wow, that's one of the more singular guitar faces, forgot about his teeth

Do you want the function of the synth?

Or just that particular sound? Because if it's just the sound I think you could get really close by turning the guitar into a square/tri wave and then using a LPF to get that "soft focus" sound, then more distortion to add artificial "presence" to get some definition and articulation back. You would have way more sustain, and less fretboard/finger sound (read: less human, more synth). Maybe some CMOS stuff going into a gyrator going into more CMOS stuff? If you only want that sound I would say forget about tracking, gate/triggers, etc.

From that old thread, the legendary Tim Escobedo (emphasis is mine):

The F to V chip is a possibility. I think the real difficulty will be getting the VCO to scale correctly with the F to V chip output. In the synth world, pitches are usually scaled in 1V/octave, which makes interfacing easy, but requires sometimes very complicated circuitry to translate exponential scale to a otherwise linear VCO. And you'll probably have to drive the F to V chip with a comparator output anyway, as I think they usually want a clean square wave to track.

That's the CMOS square/tri thing. Assuming you only want one sound, the only thing that would be better about triggering a VCO with the guitar instead of just processing the guitar's signal would be infinite sustain. But if you get that, then you have the challenge of generating and sending an "off" signal with a guitar.

I'm really looking for that sound, just a one trick pony. I have the tri-square wave thing at the output but a really weak signal... and I have to amplify the hell out of the signal going thru the LM2917 just to get that. I'm still working on that part but I was kinda thinking the same thing about some kind of tone control to shape all that stuff at the output. Hadn't thought about presence but I think you're probably right about that.

Hmm... that gives me a few more ideas to toy with.

[Paul Marossy]

Didn't the "Trombetta" modification to the Jordan Bosstone do that?

Never heard of that one. But I do have a Boss Tone lying around in moth balls...

[Mark Hammer]

The 1:50 mark here: https://www.youtube.com/watch?v=78XVvOXcecY

This thread: https://www.diystompboxes.com/smfforum/index.php?topic=85309.msg712902#msg712902

The tone is a little rougher than what Metheny gets, but a bit of filtering might nail it.  The envelope seems about right, though.  And certainly less costly or troublesome than doing P2V.

[Paul Marossy]

The 1:50 mark here: https://www.youtube.com/watch?v=78XVvOXcecY

This thread: https://www.diystompboxes.com/smfforum/index.php?topic=85309.msg712902#msg712902

The tone is a little rougher than what Metheny gets, but a bit of filtering might nail it.  The envelope seems about right, though.  And certainly less costly or troublesome than doing P2V.

Interesting! I think you're right, my circuit has gotten pretty complex and it STILL doesn't work lol.

Seems like with some strategic filtering I might be able to get something I can live with.

Where is the info on the mod itself though?

[Mark Hammer]

It's probably somewhere in the archives here.  You'd need to look for Jordan Boss-Tone.  Not unless Sir James P. Photon, Doug Hammond or Rick Holt have the info handy.

[Paul Marossy]

OK, thanks Mark.

Hmm.... for that matter, I wonder if my original EH POG could get something like that. I can get steel drum-like sounds with it, but never thought about maybe getting some various overtones that might mimic a horn with it. I'm sure that I probably need something else in conjunction with it... probably a smooth(er) sounding dirt pedal?

[Marcos - Munky]

Schematic
https://www.diystompboxes.com/smfforum/index.php?topic=70080.msg726155#msg726155

Layout
https://www.diystompboxes.com/smfforum/index.php?topic=70080.msg726155#msg726155

Another layout
https://www.diystompboxes.com/smfforum/index.php?topic=70080.msg866069#msg866069

The 47r resistor should be 470r actually.

[Paul Marossy]

Schematic
https://www.diystompboxes.com/smfforum/index.php?topic=70080.msg726155#msg726155

Layout
https://www.diystompboxes.com/smfforum/index.php?topic=70080.msg726155#msg726155

Another layout
https://www.diystompboxes.com/smfforum/index.php?topic=70080.msg866069#msg866069

The 47r resistor should be 470r actually.

Thanks! I will play around with this and see what I come up with.

[ElectricDruid]

Aside from being played from a guitar, it sounds like a fairly straight-forward analog "synth brass" sound. Those are usually a couple of rich oscillators (squares or ramps) and a nice "honky" filter. The "honk" implies some resonance, and plenty of movement, so either a triggered envelope or an envelope follower, or a bit of both. It could be a 12dB/oct filter (a la Oberheim) or it could be a 24dB/oct filter (a la everyone else, including Roland).

I think you'd get close with some synthy square wave fuzz sound, particularly if it provides several octaves to mix together, but the filter is going to be the key. Roland's synth filters are mostly 24dB/oct (e.g. 4 stage) OTA-based cap-to-ground designs with a FET used as the buffer. They had proprietary chips for this, but they're just four OTAs and a simple exponential convertor in a chip. This is nothing you can't build with a couple of LM13700s and a few FETs and transistors.

The details of the filter envelope are more obscure. Do we have any idea what the controls on this guitar synth look like? That would give us a few clues as to whether it's an envelope follower or a triggered synth envelope. For "maximum synthyness" it probably wants to be a triggered ADSR type thing. But for more expression an envelope follower would be preferred. Which is why I'd have both if I was designing the thing. However, I don't know which way Roland went...

HTH,
Tom

[stallik]

Guitar to iPhone adaptor in a Stompbox then MidiGuitar driving sound tank. Nothing like having a purpose build Stompbox to give you this sound but plenty for me to play enough with it to get bored and move on. Underwater bagpipes are still fun though

[Paul Marossy]

The details of the filter envelope are more obscure. Do we have any idea what the controls on this guitar synth look like? That would give us a few clues as to whether it's an envelope follower or a triggered synth envelope. For "maximum synthyness" it probably wants to be a triggered ADSR type thing. But for more expression an envelope follower would be preferred. Which is why I'd have both if I was designing the thing. However, I don't know which way Roland went...

Don't know the answer to that but your suggestions mirror what's outlined in this interesting document: http://www.eecs.ucf.edu/seniordesign/fa2010sp2011/g18/docs/VRS-1.pdf?fbclid=IwAR2r8145d-8ul9UHQ-kPrP6Q_4pREf41RxTctWVdC7YuzNIszzaMjT6KK5k

[Paul Marossy]

Guitar to iPhone adaptor in a Stompbox then MidiGuitar driving sound tank. Nothing like having a purpose build Stompbox to give you this sound but plenty for me to play enough with it to get bored and move on. Underwater bagpipes are still fun though

Ha ha, I'm still in the guitar stone age over here bro 

[ElectricDruid]

A few searches suggest that he was using the GR-300 synth + GR-303 guitar combination.

https://www.joness.com/gr300/GR-300.htm

The site includes plenty of details of the analog synthesis, including the "trumpety" quality, and a schematic:

https://www.joness.com/gr300/service/G-303_G-808_GR-300_SERVICE_NOTES.pdf

This gives some answers to the queries. Firstly, the thing is hexaphonic, and uses a hexaphonic pickup. So any attempt to copy it with a normal guitar with a normal pickup is doomed to failure without serious DSP horsepower behind it. Also it's "paraphonic", that is to say it uses multiple oscillators for the different note pitches, but routes them all through a single filter.

The synth part uses a frequency detection circuit to find the pitch from each part of the hex pick-up, and that drives an oscillator with a ramp-like waveform, which helps with the trumpety/brassy tone. The filter is classic Roland, based on their IR3109 chip, as used in the SH101, Jupiter 8, Juno 6/60s and others. The envelope is an envelope follower, but there's a comment on the site about the way that the pick attack of the guitar makes the envelope follower give an initial "splat!" which sounds a lot like the initial chiff sound of brass instruments. I don't understand at first glance where that comes form or how it's done, but the information is in there somewhere.

Tom

[Paul Marossy]

This gives some answers to the queries. Firstly, the thing is hexaphonic, and uses a hexaphonic pickup. So any attempt to copy it with a normal guitar with a normal pickup is doomed to failure without serious DSP horsepower behind it. Also it's "paraphonic", that is to say it uses multiple oscillators for the different note pitches, but routes them all through a single filter.

The synth part uses a frequency detection circuit to find the pitch from each part of the hex pick-up, and that drives an oscillator with a ramp-like waveform, which helps with the trumpety/brassy tone. The filter is classic Roland, based on their IR3109 chip, as used in the SH101, Jupiter 8, Juno 6/60s and others. The envelope is an envelope follower, but there's a comment on the site about the way that the pick attack of the guitar makes the envelope follower give an initial "splat!" which sounds a lot like the initial chiff sound of brass instruments.

Yes, I am aware of the hexaphonic pickup. I'm only trying to approximate that sound. After a little research today I can see that really the best and most reliable way to do it is with a hexaphonic pickup and grouping all the possible frequencies into basically six groups and then processing each one of those separately.

He's been using that synth for a long time, I'm sure it's probably the combo you suggest.

So with a hexaphonic setup, can you play full chords and not have any weirdness? I've only heard him doing single note kinds of things with that synth. I'm just wondering if you might get intermodulation distortion or something like that. I'm supposing not since Roland does stuff top notch and is well engineered.

[ElectricDruid]

Exactly. The point of the hexaphonic pick-up is that each signal is only a single string, so you've only got a single fundamental frequency on each one (making frequency detection a lot easier) and you can feed each one to a fuzz stage and mix them back together and get no intermodulation distortion.

Still, for single note lines it shouldn't make much odds. So it's worth a shot. You could do a "single channel" version that used basically one voice from the Roland system, followed by the paraphonic filter and VCA and it'd give you the sound, as long as you stayed off the chords.

Reading a bit more about it, the "VCO" is interesting. It seems to be a basic integrator which is reset by the incoming frequency. This means that the waveform is a clean ramp, but the amplitude varies with frequency (halves for each octave higher). Roland's solution to this is to clip all the waveforms to the same height. The result is that the the waveform changes shape and harmonic content across the range of the instrument...just like a lot of acoustic instruments, in fact.

There's quite a lot of interesting things in that schematic. Thanks for bringing it up. I'd never have thought to look at it otherwise.

Tom

[Paul Marossy]

You could do a "single channel" version that used basically one voice from the Roland system, followed by the paraphonic filter and VCA and it'd give you the sound, as long as you stayed off the chords.

That's an interesting idea.

Reading a bit more about it, the "VCO" is interesting. It seems to be a basic integrator which is reset by the incoming frequency. This means that the waveform is a clean ramp, but the amplitude varies with frequency (halves for each octave higher). Roland's solution to this is to clip all the waveforms to the same height. The result is that the the waveform changes shape and harmonic content across the range of the instrument...just like a lot of acoustic instruments, in fact.

There's quite a lot of interesting things in that schematic. Thanks for bringing it up. I'd never have thought to look at it otherwise.

Tom

That makes sense with my limited understanding of all this stuff. I see the big picture though. This is interesting stuff indeed.

[Mark Hammer]

The Youtube that you originally linked to was all single-note stuff, which is why I thought "Why get into all that divided pickup stuff when that modded Boss-Tone seems to approximate it well enough for single-note runs?".

I have a GK-1 pickup and a companion GM-70 that I've never really bothered to learn much about.  I also acquired former forum member Peter Snow's Casio MG-510 guitar that lets me simply run a MIDI cable to a tone generator and be done with it.  In both cases, however, the pickup has to be situated very near the bridge, and you have to adapt your picking style.  Don't get me wrong.  I love guitar synth, but if a little modded 2-transistor distortion gets you to where you want to go, I say vaya con Jordan.