Theremin mixer / tone generator - Original idea?

I have just spent this weekend absolutely absorbed with an idea I had.. Testing it in simulations, building crude proof-of-concept breadboards.. It was one of my Eureka moments.. Then came the downer.. What do I do with this? Apply for patents and lock it away? - I aint got the money, time or inclination for that right now..
I have decided to release this idea for public scrutiny.. I may regret this move, if it turns out to be a real winner.. But I have plenty of other ideas, and until I get people believing that I am not just a load of hot air (actually, I have been feeling that way about myself lately) these ideas go slowly, or nowhere.

New-Theremin-Tone-Generation.pdf (http://www.scribd.com/doc/6515555/New-Theremin-Tone-Generation) takes you to my 7 page, quite technical document. I invite everyone with an interest in the innards of Theremins to look at it, and give me feedback.

I am also looking for design / consultancy work at the moment, as I am going broke.. so hope this might be seen by some potential client / employer / backer.

Uh, I'm a man in need of a metaphor.

I've read your document, and I think I kind of get it, but I'm not sure.

Here's the gist, in as few words as possible.

It's a stroboscope for audio.

I'm thinking of rotating cart wheels in movies - the apparent rotational speed is a function of the actual speed and the rate at which frames are captured. So as we sample a waveform periodically we build a new waveform related to the original waveform and the periodicity of the sampling?

Was I anywhere close?

Gordon, that is how I'm reading it.

One of the issues with a/d conversion is aliasing
http://en.wikipedia.org/wiki/Aliasing and, I get the impression that the theremin-mixer proposal is to purposefully use aliasing to create an audio frequency signal.

I just skimmed the article, though... I am sure there is more to it than that.

Interestingly, the vacuum tube mixer/detectors worked a little bit like an AND gate -- that is, it "caught" the top of the resultant signal from mixing the two RF signals. Note that the RCA theremins and Clara's theremins sound buzzy compared to, say, the Theremax which uses a ring modulator to extract a sine (or nearly sine) wave.

GordonC: “the apparent rotational speed is a function of the actual speed and the rate at which frames are captured.”

kkissinger: “I get the impression that the theremin-mixer proposal is to purposefully use aliasing to create an audio frequency signal.”

Thank you both! Both are correct.. And what astounds me is that I have had MAJOR problems getting other engineers to comprehend my related “[b]A[/b]nalogue [b]F[/b]unction[b] D[/b]uplicator” – they just don’t see it! I have (under NDA) managed to present the AFD concept to 2 big manufacturers (The AFD, as well as having uses for waveform duplication, can also duplicate other functions such as log/exponential curves / functions, and one can copy a function from say a log amplifier, and clone multiple independent instances of this amplifier .. each ‘clone’ costing a fraction of the log amplifier or other function generating circuit).. But no one understands it enough to be interested.

One question which may come up, is “why bother” to use my Theremin Mixer idea.. What advantage does it have? The best answer to this is that performing wave-shaping on a waveform which is at constant frequency, is far easier than doing so on one where the frequency is changing.. For example, if one processes a fixed frequency ramp wave with a series of bandpass filters (with, say a graphic equalizer) this can be constructed simply.. To do this on a waveform who’s frequency is changing, would require tracking the fundamental frequency, and using this tracking signal (voltage or whatever) to control the center frequency of every bandpass filter (each would need to be a VCF).

And it now looks like I may have made some big errors on this idea..

Replies from "The place that cannot be named" (Levnet) have almost convinced me that this idea will suffer from aliasing, just like digital audio..

This may not (probably does not) mean the idea is completely unworkable, but it does mean that I will need a lot more care in the design, and that there is a possibility that the sound will not be as clean as I had hoped.. Alas, digital signal processing and related (or due to related) maths is a weak area for me..

Ok, let me give you a little business advice. When you have a product or service you're trying to sell, you need to be able to give what's called the "elevator speech" about it.

Imagine you just got into an elevator with someone who has the power and money to turn your product from an idea into reality. You're going a few floors and there are several stops before you or he will get out. You have 30 seconds to explain your idea, what it is and why it's worthwhile, to this person before he gets off the elevator, and if he's not convinced by then he's going to walk away and you've lost your one chance. Can you describe your product in that time and convince him it's a great idea?

You need to be able to make that kind of case for your idea. I read this page about it and I have no clue what it does. If you can't describe it simply, nobody will buy it even if it's wonderful, because they just won't know what it is or what it does.

Tom speaks wisely.

The aliasing: (and another opportunity to air my ignorance) Would it not be easy to smooth out the steps in the waveform with a low pass filter set above the audible range?

Thank you Tom and Gordon..

"From: Undisclosed location without Dick Cheney" LOL! Never noticed that before!! :))

Tom - You are absolutely right.. And this failure is probably why I am always broke! - But this is just who / what I am.. I have tried to correct this, but fail abysmally.. When I try to 'simplify' thing, I seem to always pick the wrong 'targets'.. ie, people who do not need simplification, and when I 'go technical' I pick the wrong 'targets' and it goes over their heads.

I also present ideas as honestly as I can - Which is a mistake - as I give details of possible areas of doubt / uncertainty.. It seems that people are willing to invest 'ignorantly' but not interested if the 'full picture' is presented, warts and all.. I cannot change this - If I do not give the fullest possible disclosure, I feel dishonest.

You did give me an idea though, Gordon, with your "in need of a metophor".. Perhaps if I look for metophor in things which I understand, but others might not, and present this 'metophor' before I go into long-winded technical disclosure, I MIGHT manage the 'elevator' bit better! Your "Audio Stroboscope" was a brilliant simple way to aid understanding of the concept - If I could manage to do this kind of 'simplification' my life might become less frustrating!


With regard to Filtering.. I actually think that this core idea will work, and that the aliasing problems will not present as 'real' audio artifacts - particularly if I add a little more filtering.. Only the extremely high harmonics will be lost by doing this, and These are not too important for a Theremin.. And if they o prove to be important, they could be added back from the 'raw' (unsampled) difference square wave.. So I have not lost hope or given up...

But I did overlooks these potential problems, and make some mistakes in my original analysis.. so feel I need to alert people that there is still work to be done, and its not all 'in the bag' as I had previously thought.

Even though the concept may suffer from aliasing effects (as we discussed on that "place that shall not be named :) ), it might none the less make an interesting musical instrument in the same sense that distortion effects make for interesting guitar sounds.

So I would say build it anyway and listen to what it does. A former place of employment had a great sign on the door leading into the engineering lab: "Caution: The laws of physics no longer apply beyond this door!"

Maybe even doing something a bit in between what you propose and straight heterodyne ... ie. run the fixed reference oscillator through "effects" prior to mixing it with the pitch oscillator. Of course you will have to "redesign" those effects for higher frequencies.

Don

"Maybe even doing something a bit in between what you propose and straight heterodyne ... ie. run the fixed reference oscillator through "effects" prior to mixing it with the pitch oscillator. Of course you will have to "redesign" those effects for higher frequencies."

Having a fixed frequency 'reference' waveform allowed this waveform to be processed at will - one could distort it, filter it, do what the hell you wanted to it .. And (I believed) this would 'reflect' on the audio which came out..

I have been studying the related DSP theory after you guys at the "place" shocked me out of my daydream.. and my head is swimming in a bog of nasty (most completely incomprehensible - some could be hieroglyphics for all I know.. nope – in fact I think I would understand it more if it was hieroglyphics ): maths and theory…

But.. From what I can understand, I think most problems would occur at the higher harmonics, which would be ‘reflected’(that word again.. there must be a better one) down into the audio band. My original idea for the master reference waveform was to generate an additive mixer, with variable amplitudes for fundamental and the first 5 or 6 harmonics.. Then I got more ambitious and thought of making the reference oscillator/waveform a function generator giving mixable square, ramp and triangle waveforms, and having this followed by a filter with variable frequency and Q.. With this, I could generate any waveform ..

I think my original idea will be less likely to cause problems .. It does not give the unlimited range of sound shaping of the latter – but I have played with (in simulation) the 6 harmonic mixer, and it produces some wonderful sounds.. I think waveforms like square and ramp are just asking for trouble – and I have managed to run a few simulations and taken their output directly to my PC soundcard, and the six-harmonic mixer sounds sweet – but the squares and ramps have nasty distortions.
but this is just simulation - reality may be different!