Hexaphonic Project

[psw]

All the clips I've heard have been saturated in effects...any chance of hearing the actual guitar clean without anything on it? Traditionally these things are judged by what they can do as a basic sound that can be 'effected'...plus, it's easy to be impressed with the computing power or digital processing these days, but that isn't what is being demonstrated. Holding a note or chord indefinitely is after all not hard with sample and hold technology in the digital realm without any modifications...as is pitch shifting and filters...but working with the sound of a real guitar, now there's a trick.

But it's good that you are enjoying the process, where ever it may lead and it is giving you some results...carry on...

[McSeem]

Psw, you will hear it. All in good time :-)

The reason is, in my initial experiments I just want to hear what I put to the driver coils. Then. The non-linear voltage tranfer characteristic is the simplest thing that provides some degree of low coil power plus stability at the same time. In my previous experiments, the direct signal, combined with a high-Q resonance system (which guitar strings are) just goes wild. That's OK, just as planned. I have a suspition that in mono systems, there's just a natural power restrictrion - the 9v battery simply cannot provide so much power, and that's why a simple battery-powered sustain is getting stable. Works like a "natural dynamic range compressor". In my case I have no power restrictions, I can easily melt the coils and break the strings.

And, BTW, the sound is not completely saturated. It's not like square, it has almost perfectly round peaks. However, the fronts and backs of the waves are almost vertical, which also sounds harsh and saturated. Anyways, I am a "nut scientist", I'm just trying to experiment with different crazy ideas. But I'm not totally nut, if I fail, I'll admit it.

Also, there's a big frustration about MOTU 8pre audio interface. It's total crap, I'm totally disappoined with it. I ordered another device, Saffire PRO 40, which is inexpensive and has very good responses. It's time to look at the "traditional quality from England" :-)

Well, the best one seems to be "the Germans" RME Fireface 800 (nom-nom-nom), but it's sooo overpriced.

[psw]

I'm not following...

Are you saying that although you can get sustain now, it is not clean?

Is it not possible to hear the guitar clean as it is working now...I mean, we are not just talking distortion here but all kinds of filtering and other effects are we not? These can be 'impressive' but surely not how you are testing the effectiveness of the device, how would you be able to hear what is going on (or people like me hear it) if everything is masked by such distortions?

You will note how much emphasis was put into "fizz" and drive wave forms for years and how to get the best clean response of the actual instrument. These are crucial requirements to deal with as if it produces it's own colour, it will colour everything you do with it also.

I have a suspition that in mono systems, there's just a natural power restrictrion - the 9v battery simply cannot provide so much power, and that's why a simple battery-powered sustain is getting stable. Works like a "natural dynamic range compressor". In my case I have no power restrictions, I can easily melt the coils and break the strings.

It shouldn't be a "suspicion" but it's good that someone is finally catching on to the subtleties of some of the simple designs I tend to promote. The restrictive power of the 9volt battery supply, the distortion compression as something like an LM386 peaks, all manner or natural results of the design provide for limiting effects so that things don't get out of control and enhance response.

It's not hard to melt coils or even fry strings and burn fingers and to pull notes way out of tune, just look at the first post in the sustainer thread about my previous attempts before starting that...not ideal!

I would have thought that getting a good clean and controlled response (through limiting) would be far more of a priority than worrying about harmonic generation and phase angles and filters and such.

But, I am a little lost as the sound clips seem not to illustrate things too well. Surely the guitar is capable of making a guitar sound free of effects so that it can be heard? I don't see how frying the coils comes into it surely...if it can do what you are already recording, surely it can do the same thing without the effects so you can hear whats going on?

I see, it "just goes wild" but that's a problem right there that needs to be addressed. Hearing what the driver hears is cool, we all do that by connecting a speaker to the circuit to 'hear it', but in the end it is how the thing works in the guitar. In short, it is hard for me to "get" where you are up to and where the thing is going or you are aiming for.

Anyway, it certainly is an expensive project and getting increasingly complex...I prefer to aim for a more 'elegant simplicity' myself, even when I was working on my Hex drivers...the intention was to get things that would inherently work and continue to simplify things so that more complexity could be added to that again as required, otherwise you can end up chasing your tail and the complexity just runs rampant. Already you seem to be requiring a computer just to generate the drive signal! For me also, there are many times where practicality has to be acknowledged...there's only so much I'd be prepared to plug my guitar into to make a noise after all!

[al s.]

McSeem. your latest soundclip is just awesome. A wonderful balanced chord sustain.

And those beautiful harmonic overtones! Is it all that sound coming from the strings?

Its hard (for me) to keep up with your technical explanations but I love the direction

that you are going, and I look forward to your posts.

[Fresh Fizz]

McSeem. your latest soundclip is just awesome. A wonderful balanced chord sustain.

And those beautiful harmonic overtones! Is it all that sound coming from the strings?

Its hard (for me) to keep up with your technical explanations but I love the direction

that you are going, and I look forward to your posts.

I'm glad to hear this from you, al s.

I was starting to think there was something wrong with my hearing. Or taste.

So much progression and innovation, and we're only at page 2!

FF

[McSeem]

I have already provided a "clean" sample: http://antigrain.com/hex_project/sample_sus_linear.mp3

In the auto-excitation mode, with a significant gain it's very unstable and tends to tear off the strings. As I expected.. So, at least a heavy DR compression is a must. So far the distortion plays role of a "dirty compression".

al s., yes, it sounds nice when playing chords, but single notes don't sound that nice. To be nice it requires a noise gate, compression, and automatic phase adjustment. As for the progress... I also have to fight with Win7, task and IO priorities, and so on. With the normal, regular settings and with small buffers, it clicks and pops as soon as you move any window. So, Win7 by default is very unfriendly to pro audio streams. I spent some time with the Win7 multimedia API, but made it perfectly, solid-rock stable, even with other tasks running that load all CPUs 100%.

[psw]

Thanks...

Are all those clicks and pops and drop outs something to do with the processing...I'm not following why it does that to the actual guitar sound, surely it would only affect the drive signal and the strings momentum would carry through?

Also seems to be generating a fair few harmonics, perhaps perhaps the square wave signal is boosting all the huge harmonic content present in the piezo system and requires filtering back to the fundamental.

There seems to be some 'winning out' in the middle range of the guitar. On mine, it's kind of 'tuned' so the middle range 'wins out' which is not a bad thing for the polyphonic effect.

I can't help but think that you'd get much the same result without the difficulties, easier and cheaper and smaller by simply going analogue, and by limiting the power not risk melting the coils. For instance, 3 stereo amps could drive each coil individually from each piezo saddle and provide the same kind of thing without using any 'computer' power at all? You could mix the power to compensate for strings as well as other tweaking as well...just an impression

[McSeem]

Absolutely. I'm in the very beginning, and I said that before:

Now about the sustainer. It doesn't yet work as I want, I only tried if it works at all. In fact, for now I only simulated a simple hexaphonic sustainer solution with a monster system, but I'm sure, with the software and DSP I can do a lot of things that you can never achieve with circuits.

That is, the first step is ONLY reproduce a simplest solution and prepare the ground for further experiments.

[McSeem]

So, I added a simple software dynamic range compressor and there's some non-distorted acoustic sound with hex sustain. First is just a plain feedback.

http://antigrain.com/hex_project/sample_su...pahse_shift.mp3

The second is with a phase shifting at random speed for different strings. You will hear some digital noise there. It's normal and expectable. It's just because I do the phase shifting without care, that is, without any interpolation between frames. The cure for that is plain simple, it's just not done yet.

http://antigrain.com/hex_project/sample_sus_pahse_shift.mp3

[Fresh Fizz]

To me it seems that the hex magnetic gives a more pleasant sounding feedback. With my own sustainer (with magnetic pickup) I don't get higher than the 3rd harmonic. The hex piezo seems to be able to give you all the higher harmonics you need.

I have some questions. OK, you might as well interpret it as a request for more sound clips

1. What is the phase relationship between the sustainer driver and the hex piezo? For a magnetic pickup it's all about position,polarity and electrical properties of the coils, what's it like for a piezo?

2. How does the sustainer device perform when a mix of hex magnetic and hex piezo is used as input? Do you get a more versatile or balanced sustainer by combining the hex mag with the hex piezo?

3. What does it sound like when the hex magnetic is used as sustainer input and the hex piezo as output (to amp or DI)? Or vice versa?

Cheers,

FF

[McSeem]

1. What is the phase relationship between the sustainer driver and the hex piezo? For a magnetic pickup it's all about position,polarity and electrical properties of the coils, what's it like for a piezo?

It's hard to tell, mostly because of very different spectrums. But I noticed, for best fundamental frequency sustain there must be different phase shift between mag and piezo. So, when I adjust the phase for piezo and then switch to mag, I have to adjust the phase differently.

2. How does the sustainer device perform when a mix of hex magnetic and hex piezo is used as input? Do you get a more versatile or balanced sustainer by combining the hex mag with the hex piezo?

I haven't yet done enough experiments, but the mix definitely affects sustain. I can't estimate it in terms of versatility or balance, but the sustain spectrum definitely differs.

3. What does it sound like when the hex magnetic is used as sustainer input and the hex piezo as output (to amp or DI)? Or vice versa?

In my design hex and piezo channels are mixed in the Graphtech preamps with two 6-pole volume pots. So, in the guitar I have only 6 channels. To experiment with different sustain source and inputs I would have to use 12 channels, which would be a total overkill. I simply don't have so many inputs in my audio interface. The signal goes through the in-interface, software, out-interface, power amps, and back to the sustainer. I already use a 24-pin dual link DVI cable. There only 14 wires that can be used for the audio signal (it has 7 separately shielded pairs). I use 7 for the pickups signal and 6 for the driver (the 7th is the neck HB). So, plus one wire for the preamp power, and I only have 4 wires left for the future on-body controls. 5 pins are used for shielding.

BTW, the new interface, Saffire Pro 40 seems to be absolutely stable. It's cheaper, better, and has more ins and outs than this shitty MOTU 8pre. And their preams sound is very good.

So, just a note: MOTU 8pre is totally incompatible with PC and Windows (I suspect it's only because of absolutely buggy software drivers). It can simply damage your power amp, speakers and even your ears. Sometimes it produces a huge wild burst of noise: http://antigrain.com/hex_project/motu_noise.mp3 (I recorded it with a USB mic from headphones). Other people also complain about it: http://forum.recordingreview.com/f93/motu-...te-noise-22921/

Although, with the OSX there were no any complains, so MOTU must be fine with Mac DAWs.

[Fresh Fizz]

In my design hex and piezo channels are mixed in the Graphtech preamps with two 6-pole volume pots. So, in the guitar I have only 6 channels. To experiment with different sustain source and inputs I would have to use 12 channels, which would be a total overkill. I simply don't have so many inputs in my audio interface. The signal goes through the in-interface, software, out-interface, power amps, and back to the sustainer. I already use a 24-pin dual link DVI cable. There only 14 wires that can be used for the audio signal (it has 7 separately shielded pairs). I use 7 for the pickups signal and 6 for the driver (the 7th is the neck HB). So, plus one wire for the preamp power, and I only have 4 wires left for the future on-body controls. 5 pins are used for shielding.

Yes, the building of the hex magnetic and all the necessary circuitry inside your guitar is an impressive piece of work. I myself am thinking of a solution which enables me to stick with the mono guitar pickup. Like adding 6 coils whose only function is to sense which string is being picked/ sustaining. And filter the sustainer signal according to this information.

Basically a analogue and poor man's hexaphonic.

BTW, the new interface, Saffire Pro 40 seems to be absolutely stable. It's cheaper, better, and has more ins and outs than this shitty MOTU 8pre. And their preams sound is very good.

And it works under linux.

FF

[Hideki]

Maybe you can get some ideas from this...

This is the Moog Guitar patent: http://www.freepatentsonline.com/6216059.pdf

It's written on the back of the headstock, so it should be the right one:

http://www.moogmusic.com/forum/viewtopic.php?p=53143#p53143

After reading through it once, I still can't figure out how they can both drive and pick up the signal at the same place without losing part of the waveform when it switches from pickup to driver.

In this picture it looks like there's 12 connections coming from each pickup, so it's either two coils per string, or we are seeing both connections to the 6 coils. In that case, the 4 transistors per string may be an H-bridge to drive both ends of the coil instead of keeping one side grounded.

http://www.soundonsound.com/sos/mar09/imag...ogGuitar_02.jpg

[McSeem]

And it works under linux.

I only found this one, it's still in the "experimental" status: http://www.ffado.org/?q=node/862

So far I use Win7. It's OK for experiments, but it's not a real-time system and can't be used for any live performance or even recording. So, in future I'll probably switch to Linux.

In this picture it looks like there's 12 connections coming from each pickup, so it's either two coils per string, or we are seeing both connections to the 6 coils. In that case, the 4 transistors per string may be an H-bridge to drive both ends of the coil instead of keeping one side grounded.

http://www.soundonsound.com/sos/mar09/imag...ogGuitar_02.jpg

Hideki, thanks for the info. It looks like they use something like Pulse-width modulation, at least, at the first sight. Anyways, the processing is very complex there and the circuit board looks like a monster. I'm trying to experiment with different software approaches, which is much simpler and takes much less time for prototyping.

[McSeem]

Yes, the building of the hex magnetic and all the necessary circuitry inside your guitar is an impressive piece of work. I myself am thinking of a solution which enables me to stick with the mono guitar pickup. Like adding 6 coils whose only function is to sense which string is being picked/ sustaining. And filter the sustainer signal according to this information.

Basically a analogue and poor man's hexaphonic. laugh.gif

Hmm, it doesnt look simple either. You probably will use analog switches to connect different filters. Besides, what happens in case there's a signal from two or more strings? Just connect two filters in parallel? In my opinion it's not that hard to build a true hex system. You can order pickup coils from Paul Rubinstein, for example, and use 3 minimal-circuit stereo power amps, such as LM4952, which has a DC gain control. Not sure about namely this one, but I'm sure there's a simple and compact IC solution. No analog switches, just different filters for different channels and a single-pole sustain pot. Well, plus maybe 6 single FET preamps. But anyways, it's nothing compared to that monster circuity Moog guitar. I was truly impressed by that.

[Fresh Fizz]

Yes, the building of the hex magnetic and all the necessary circuitry inside your guitar is an impressive piece of work. I myself am thinking of a solution which enables me to stick with the mono guitar pickup. Like adding 6 coils whose only function is to sense which string is being picked/ sustaining. And filter the sustainer signal according to this information.

Basically a analogue and poor man's hexaphonic. laugh.gif

Hmm, it doesnt look simple either. You probably will use analog switches to connect different filters. Besides, what happens in case there's a signal from two or more strings? Just connect two filters in parallel? In my opinion it's not that hard to build a true hex system. You can order pickup coils from Paul Rubinstein, for example, and use 3 minimal-circuit stereo power amps, such as LM4952, which has a DC gain control. Not sure about namely this one, but I'm sure there's a simple and compact IC solution. No analog switches, just different filters for different channels and a single-pole sustain pot. Well, plus maybe 6 single FET preamps. But anyways, it's nothing compared to that monster circuity Moog guitar. I was truly impressed by that.

No, there is a fat chance nothing concrete will come out of this. After having built an ordinary sustainer with AGC I want to do something more experimental. But I want to stick with my high impedance humbuckers as signal source. My idea is to use overdrive instead of AGC and use low pass filters after the overdrive. Perhaps another way of achieving a filter effect depending on which string is played is to put a low pass filter before an auto-wah.

I understand your question about the parallel filters. But I want to keep it as simple as possible. I want the device to sustain the lowest frequency it can 'find'.

And I wonder if it's possible to build a basic mono Moog. I don't think it's pulse-width modulation. Couldn't it be time division multiplexing (and demultiplexing)?

Using an oscillator and some CMOS switches, could that work? Switch between pickup and driver function?

I only don't understand why the Moog doesn't sound fizzy while the sustainer signal is that much truncated.

Cheers

FF

[McSeem]

Just reporting...

So far there's no much progress with fancy "totally-in-control" sustain, but my project is not only about the sustainers, it's mostly about hexaphonic in general. Next step will be a fast reliable pitch detection, synchronization and controllable phase shift. It's still a long way to go. However, I'm gradually handling sound processing and having a lot of fun when I have spare time. Recently I have implemented formant filters used for vocoders, and applied them to the guitar sound. The result is interesting. The formant filters take spectral rich signal, such as saw or square and produce more or less realistically sounding vowels, o,i,a,u,e. But applied to the pickup signal it sounds very differently. I also implemented an oscillating filter that interpolates the parameters between different vowels at low frequency. It sounds like a Leslie speaker, which I didn't expect. Well, it actually sounds like 6 Leslie speakers connected to the respective strings.

So, this is a sample of pure formant signal:

http://antigrain.com/hex_project/sample_os...ant_filters.mp3

But it sounds too fat, so, I decided to mix the result with the undistorted input:

http://antigrain.com/hex_project/sample_os...mant_mixed1.mp3

Yes, there's a hex sustain too, I feed the coils with the filtered formant signal.

The next is taken from piezo saddles, with NO SUSTAN, but with huge formant input gain and distortion. The bridge saddles are so sensitive that with these parameters you can hear some noise at the end. The noise is produced by my heartbeat. Really! It's not a joke.

http://antigrain.com/hex_project/sample_os...mant_mixed2.mp3

Different parameters, with mostly magnetic hex, and with a bit of piezo mix (also no sustain at all):

http://antigrain.com/hex_project/sample_os...mant_mixed3.mp3

With a simple slight noise gate and a lot of sustain:

http://antigrain.com/hex_project/sample_os...mant_mixed4.mp3

Some single notes with heavier noise gate and also a lot of uncontrolled sustain:

http://antigrain.com/hex_project/sample_os...mant_mixed5.mp3

Sorry for non-artistic playing. But note all is processed in REAL TIME, with very low latency, less than 10 milliseconds.

So, my point is. After some initial efforts I can easily implement a lot of fancy effects in software and it's going to be all hexaphonic. The effects are so simple to implement and there's a plenty of algorithms, thousands of them.

[col]

And I wonder if it's possible to build a basic mono Moog. I don't think it's pulse-width modulation. Couldn't it be time division multiplexing (and demultiplexing)?

Using an oscillator and some CMOS switches, could that work? Switch between pickup and driver function?

I only don't understand why the Moog doesn't sound fizzy while the sustainer signal is that much truncated.

hmm... thinking out loud time...

does the signal in the moog go straight from pickup to amp, or does it go through some dsp that 'reconstructs' it ?

if the pickup signal is only sampled while there is no sustainer drive present, then the switching frequency can be removed as it is a known quantity. The 'holes' in the output could then be removed either with filtering or some sort of dsp using interpolation or some such...

I suppose the crux is how high the switching frequency can be. I guess this depends on how quickly the field of the driver/pickup can be collapsed and reconstructed. For the system to work with an analog output - like a traditional guitar - the frequency would have to be high so that any switching noise can be filtered out without impacting the guitar tone....

[Fresh Fizz]

But it sounds too fat, so, I decided to mix the result with the undistorted input:

http://antigrain.com/hex_project/sample_os...mant_mixed1.mp3

You could try to use less overdrive/gain. That way you can vary the sound a bit more by changing the way you hit the strings (soft/hard picking).

The next is taken from piezo saddles, with NO SUSTAN, but with huge formant input gain and distortion. The bridge saddles are so sensitive that with these parameters you can hear some noise at the end. The noise is produced by my heartbeat. Really! It's not a joke.

http://antigrain.com/hex_project/sample_os...mant_mixed2.mp3

a case of lack of practice. More callus will keep the heartbeat away

So, my point is. After some initial efforts I can easily implement a lot of fancy effects in software and it's going to be all hexaphonic. The effects are so simple to implement and there's a plenty of algorithms, thousands of them.

That sounds good! How about some:

polyphonic fuzz

some extreme eq settings, like ultra deep or twangy bass strings or fixed wah wah setting per string.

Cheers

FF

[McSeem]

That sounds good! How about some:

polyphonic fuzz

some extreme eq settings, like ultra deep or twangy bass strings or fixed wah wah setting per string.

Absolutely. AFAIU, fuzz is just a matter of a proper transfer characteristic plus filtering. I can simulate any transfer with fancy math or just by interpolating a manually designed chart. For example, this function:

double gloubi_boulga_sharper(double input)

{

	double x = input * 0.686306;

	double a = 1 + exp (sqrt (fabs (x)) * -0.75);

	return (exp (x) - exp (-x * a)) / (exp (x) + exp (-x));

}

It's VERY computationally expensive (takes about 5% of the time I can afford in the process call-back), but it sounds nice, especially combined with a Bezier-based transfer chart.

http://antigrain.com/hex_project/sample_transfer01.png

http://antigrain.com/hex_project/sample_transfer01.mp3

Well, I realize it's still not "kosher", but I'm in the very-very beginning of my way. Besides, big chords with fuzz sound very differently because there's no intermod. So, with hexaphonic processing (no matter, analog or digital) you won't achieve this authentic dirty grunge sound. It's not bad, it's not good, it's just different.

[Truth_David]

What happened to this thread? Is this work still in progress? I have PM'd you.....