Guitar synth.

[demonstar]

I'm wanting to make a guitar synth. What I'm after is a sine wave oscillator that tracks the pitch of the guitar input. I've explored the idea of guitar to cv devices such as some of the Penfold stuff however Theres reports that they aren't great and are unstable in nature. I came across this schematic posted on another forum (electro-music) by stephen giles...

"http://img.photobucket.com/albums/v317/StephenGiles/EH_sine.gif"

Am I correct in believing if I feed a guitar input directly into this circuit I will produce a sine wave (where labelled on the diagram) of the same frequency as the guitar input?

If that is the case I wish to use that as an oscillator for a synth. I believe that would produce some amazing sounds in such a way. The rest of building/designing a synth (or at least piecing different sections together  ) is well documented on the internet. By this I mean other synth sections as in filters etc.

The whole theory behind this is I'm wanting to build a synth that can play a melody however I am unable to play the keyboard. So I'm after a synth that can track the guitar pitch and produce synth tones. A nice target would be something vaguely similar to "gates of Babylon" by rainbow. Or any other rainbow or Uriah Heep etc for that matter.

Thank.

[Mark Hammer]

Producing a sine wave has never really been the objective of many synths.  The reason is that analog synthesis operates on the basis of subtractive synthesis.  That is, you start out with a waveform that contains many harmonics of the fundamental, and you "sculpt" sounds by carving those harmonics away in some selective fashion over time.  A sine wave HAS no harmonics itself (unless it is a poor version of a sine wave with imperfections), so there is nothing really to filter away. 

Ultimately, what you want is some means of tracking pitch and deriving a reliable control voltage that represents the note pitch.  The control voltage would then control an oscillator of some type that would produce several different waveforms (sine, triangle, square, ramp, variable pulse-width, etc) that produce different sources of harmonic content to combine and carve away with filters, etc.  Probably the only context where a pure sine-wave output would be "interesting" might be the case where there is some glide/glissando inserted so that the tracked output "slides" from note to note, in a manner you can't always do with mere guitar alone; sort of a low-tech version of what some players like Joe Satriani will do with a Whammy pedal.

On the other hand, if you take a sine wave and process it further (e.g., with suitable comparators, integrators, etc) you can convert the basic sine wave into something else that does have more harmonic content, suitable for filtering.  There are a number of schems posted around for various sorts of waveform conversions.  At one time, it seemed that the summer circuit collections in Elektor were about 20% waveform conversion circuits.  Whether the circuit you link to, in tandem with waveform conversion circuits is an easier-to-implement solution than a P/V unit like the Penfold project I have posted on my site ( http://hammer.ampage.org/files/GuitarP2V.PDF ) in tandem with one or more of the various VCO projects posted around the DIY Synth sites, is another matter that I leave to you to judge.

Whatever you do, please note that both the Penfold project and the E-H synth extract that Steve posted are BOTH MONOPHONIC.  That is, they can only track one note at a time and require adaptations in your picking/playing style and signal quality for optimum performance.  These are not insurmountable odds, but by no means consider this a plug-and-play scenario.

[demonstar]

Thankyou very much Mark. The reason I'm after a sine wave is I figured It'd probably be easier to transform into other waveforms than say a squarewave would be.

I assume from your response that the circuit extract should track the pitch of the guitar in the form of the sine wave. I don't mind at all that it would be monophonic and don't mind if it's not perfect. I just want to explore the world of synthesisers with my guitar and work on a good diy project.

When you said, "adapt your playing style", what exactly did you mean?

Once again thankyou very much!

[Mark Hammer]

When you said, "adapt your playing style", what exactly did you mean?

1) The circuit is desperately trying to determine what the note is amidst all the hiss, finger glisses, finger vibrato and many many other sources of sound coming through the pickups and out the jack.  Although the miracle of human perception permits us to hear the "note" through all the crap accompanying it, the way that a sheepdog can see things despite all that hair hanging in front of its eyes, the circuit is not quite so forgiving.  The user has to do whatever they can to suppress all sources contributing to the overall input signal, whether it be finger noise, hum, or the tail end of notes on adjacent strings.  Think of it like putting blinders on the detector circuit so that it pays attention ONLY to what you need it to pay attention to.  That means not only the best quality signal you can provide it, but clean picking and nimble muting of whatever you are NOT picking at this moment.  Many of these issues have been addressed in more recent guitar synths, but this ain't no 2007 circuit.  Read what people had to say about the earliest guitar synths.

2) Figuring out what note THIS one happens to be involves some determination of where the waveform peaks are and what the time gap is between them.  Because pitch = wavelength, that means that lower notes take longer to figure out than higher notes.  Sometimes on the order of several milliseconds, or enough to produce perceptible delay, and the sense that the device is not responding perfectly in time with one's picking.  That also means that picking speed needs to be slower the lower down you go.  Not molasses slow, certainly, but don't expect to be able to play "Flight of the Bumblebee" on the wound strings.  As well, certain types or speeds of string bends may throw the tracking off a little.  This is probably going to sound wrong, but the optimum playing style for circa-1980 guitar-synth technology is the Ventures on heavy-gauge strings; i.e., precise melodic picking with few bends.

All of this is not to say it CAN'T sound good.  It can sound mindblowingly good.  Just don't thing that whatever works for getting your ya-yas out will map perfectly onto use of a P/V tracking device.

[demonstar]

I think I'll give it a go and breadboard just the above circuit and see how well it tracks the sine wave before commiting.

I found these samples and if it could track similar to these clips I'd be happy. I just want something to build thats a bit different and fun...

"http://electro-music.com/forum/topic-14921-50.html"

I'll experiement a bit too .I wonder if adding an aggresive noise gate with a compressor before would help. I'll check it out.

Once again thankyou for you time and help. I'll see if I've got the parts and if not I'll get them in. I'll let you know how it goes.

[Mark Hammer]

I wonder if adding an aggresive noise gate with a compressor before would help.

Probably.  And it's hard to think of a better device for that purpose than the SSM2166.  It has a great compressor/limiter AND a downward expander type gate, all on a single DIP.  Expensive for a chip, but dirt cheap for what it does so bloody well.  You can get them at Small Bear.

BTW, thanks for the link.  Nice to stumble onto some folks working with the Penfold project.  I have two of them built but have never installed them into a chassis or fired them up.    Time to get moving I guess.

[StephenGiles]

I'm wanting to make a guitar synth. What I'm after is a sine wave oscillator that tracks the pitch of the guitar input. I've explored the idea of guitar to cv devices such as some of the Penfold stuff however Theres reports that they aren't great and are unstable in nature. I came across this schematic posted on another forum (electro-music) by stephen giles...

"http://img.photobucket.com/albums/v317/StephenGiles/EH_sine.gif"

Am I correct in believing if I feed a guitar input directly into this circuit I will produce a sine wave (where labelled on the diagram) of the same frequency as the guitar input?

If that is the case I wish to use that as an oscillator for a synth. I believe that would produce some amazing sounds in such a way. The rest of building/designing a synth (or at least piecing different sections together  ) is well documented on the internet. By this I mean other synth sections as in filters etc.

The whole theory behind this is I'm wanting to build a synth that can play a melody however I am unable to play the keyboard. So I'm after a synth that can track the guitar pitch and produce synth tones. A nice target would be something vaguely similar to "gates of Babylon" by rainbow. Or any other rainbow or Uriah Heep etc for that matter.

Thank.

Yes!

[snufkin]

im throwing the penfold p2v circuit together in the next couple of moths (if i get time) to control my sn voice
ive got most of the parts and the board etched
over at electro music i hear there are a few bugs (which have been sorted)

so if any one finishes up in the near future it would be lovely so see a build report or just i pic and some sound samples

[demonstar]

Hey chris, thats not a problem. I'll report back how it goes however I am going to make the circuit schematic I first posted. I'm going to do little bits here and there over the next few weeks to a month so it may be finished within a week or it may be a month. It depends on how much free time I have available. I'm going to have to order the ca3080 and the ca3094 as they seem few and far between.

I'm going to see how well the circuit tracks a sine wave before commiting to anything further. I have ideas of what I'll put after that circuit if it works but I'm just taking it a bit at a time.

[StephenGiles]

Nothing tracks the sine wave, the input signal is converted to a sinewave, having been compressed and processed by the adaptive filter. The VCOs in the synth track the input frequency later in the circuit - one fixed an octave above and the other two however set.

[puretube]

HighTime for a brandnew generation of more uptodate analoguous guitarsynthing... 

[demonstar]

I understand what your saying thanks Steve. I think thats what I meant it just didn't come out right. I've been thinking too and I think maybe I'm jumping in a little deep so i think I'll take some advice I've been offered in a pm and go for the guitar synth at musicfromouterspace. I understand it isn't pitch tracking but I've listened to the samples and I really like them. I think it could work better for me with it being well documented and all in one place from a very reliable source. Also a big disappointment I found with the schematic I originally referenced was the fact that the parts aren't locally available. The parts being local is important to me because local means cheap.   Soon as I have to shop abroad for parts it becomes so much dearer and takes a lot longer for them to arrive. I believe farnell stock everything I need and it's free delivery (very swift).

Anyway thankyou very much to everyone thats helped me and given advice! I really appreciate it! I'll report how my build goes which ever I go for (I guess the guitar synth at MFOS makes most sense so I'll probably choose that.).

[puretube]

for me,
local is expensive;

and the further abroad,
the cheaper... 

[snufkin]

or me,
local is expensive;

and the further abroad,
the cheaper...   

yep mostly thats true for me as well

feels kid of rubbish doesn't it


still i got most of my parts for my p2v unit 10 min down the road