Basics of how the EW-Pro works.

@Fred ...

I think I might know which 2 transistor theremin you were talking about. I think the challenge there was to try to build a usable theremin from Radio Shack parts more than anything. And now that RS has almost completed its conversion to just-another-cell-phone-store, it's just not possible to build something like that without going to other vendors.

Having something very simple and inexpensive to build as a starting point of study isn't so bad. It's the journey, not the destination for us builders and experimenters.

If you wanted to build something that is playable in a professional setting, it no doubt is cheaper to go buy an Etherwave kit than to try to develop a working and playable theremin!

[i]"I think I might know which 2 transistor theremin you were talking about. I think the challenge there was to try to build a usable theremin from Radio Shack parts more than anything. "[/i]

[b]NO! - I certainly was not talking about the RS Theremin[/b].. or most of the other low cost theremin designs/kits which people put out on the web with schematics for others to build or experiment with.. I think all of these are laudable even if only for educational purposes.

I am talking about comercially available "theremins" which are advertised as "the real thing" using a sales pitch which include phrases like "Analog Theremins will have oscillator coils" and "'Theremins' that show a nice looking wave form are simply audio oscillators" "Digital theremins have overtones which cause them to sound off key" "Digital theremins have only 18 inch playing range" and comparing their "theremin" to something like the B3 and implying that their piece of cr*p (despite it being a two transistor pitch only board) is superior! - and not puting their schematic on the web.. so potential purchasers are conned into believing that the product is something special - when, in fact, there are a myriad of equal (and better) circuits available free. I am not saying that every manufacturer should disclose their technical secrets - But I do feel that the combination of hype, denigration of other superior products, and non-disclosure (of circuits which are extensively available in the public domain, and which they have merely copied, with no added innovation or special features) makes advertising of this kind unsavory.

The "theremin" manufacturer I am refering to above is one of the worst I have seen for these tactics - but there are others.

[i]"Have you or anyone else looked at the output of the mixer in various designs with a FFT analyzer? I wonder what the differences in harmonics would be. Since there are lots of harmonics in squarewaves, maybe the mixer output would be richer in harmonics for the CMOS design than an analog one?" - Don[/i]

Yes I have, quite extensively..
The major difference is not the "waveform" per se.. it is pitch (and sometimes amplitude) dependent changes to the waveform which make the difference with analogue theremins.. The primary source of these wavform changes (and therefore harmonic content) is the interactions between the variable and reference oscillators - What defines the 'natural' tone of a Theremin is primarily a function of oscillator coupling, and it is a tricky area to get 'right' as oscillator coupling affects linearity and can cause jittery lock-up when the difference frequency is low..

With digital heterodyning, none of the harmonics
generated due to oscillator interactions, are available (particularly if the digitized oscillator waveforms are passed through dividers so that any differing mark/space which may occur as a result of converting a 'mis-shaped' analogue signal to digital are also lost) - one ends up digitally heterodyning signals with fixed M/S ratio. It is this, and probably only this, which makes (IMHO) analogue heterodyning of analogue signals superior to digital (or for that matter analogue) heterodyning of digital signals.

The normal way of digital heterodyning is by using an XOR, which produces, after minimal filtering, a triangle wave output - this waveform is easily converted to sine.. And, if one has a VCF tracking the pitch, dynamically changing from triangle to sine is easy..
One can also synchronously convert the triange wave to a ramp wave, and can generate a square wave either by feeding the triangle through a comparator or by using my D-Latch method.. (you can also do far more elaborate waveshaping by, for example, varying the angle of slopes of a waveform generated by linear inegration, or by having adjustable pulse width generated by feeding the triangle into a comparator whos reference is adjustable) So, from basic digital heterodyning one has a fair number of possible source waveforms.. comparable to the waveforms available from standard synthesizer VCO's..

And, as with Voltage controlled synthesizers, if you have VCO waveforms and a controller tracking voltage, you can apply any form of subtractive filtering or other voltage controlled modifications at will... And the master of voltage controlled sound modifiers was undoubtably Dr Moog.

My lack of knowledge about the sound processing on the EW-Pro is almost total - And I have a lot of questions.. One of these is:
CV Tracking does not operate well below 100Hz, so tracking of bass notes would be difficult / impossible - I suspect that the filters / modifiers must therefore be locked to some fixed CV when the pitch drops below 100Hz.. meaning that tones produced in the bass register would be processed through fixed, and not dynamic processing.. but am I right? How much part does the CV actually play in the tone processing of this instrument?

[i]"One thing is constant in all theremin/car analogies...
The most likely cause of failure is the nut behind the steering wheel." - Gordon[/i]

LOL!

Back to analogies.. been thinkin 'bout this ;-)

how about Lamborghini engine which is directly coupled to a low quality electric generator, and nothing else..

This generator has voltage tappings connected to a switch in the gear stick (the range switch) which routes the generator's output (selected voltage) to the vehicles sophisticated in-wheel electric motors.

(BTW, in real life, in-wheel motors do not operate like this - they are far more sophisticated, and a command string is transmitted to them to adjust their speed / torque - which then controlls the commutation.. They wouldnt operate by changing the supply voltage - Once again, I am being absurdly pedantic, but having designed the electronics for the motors for electric vehicles cannot help myself! ;-)

[b]THIS THREAD IS CONTINUED[/b] Here. (http://www.thereminworld.com/forum.asp?cmd=p&T=4548&F=3) and reply's to the following postings can be found in this continuation..

Peter wrote:

[i]The doors to the Holy of Holies of the E'Pro theremin have been ripped asunder and the contents of the tabernacle have been revealed for Philistine eyes to gaze upon!

Am I the only one who doesn't particularly care that it was empty?[/i]

Perhaps it's more like the scene in Indiana Jones And The Last Crusade where it turns out that the Holy Grail is just a simple earthenware jug and not a solid gold, emerald encrusted goblet after all.

Fred wrote:

[i]CV Tracking does not operate well below 100Hz, so tracking of bass notes would be difficult / impossible - I suspect that the filters / modifiers must therefore be locked to some fixed CV when the pitch drops below 100Hz.. meaning that tones produced in the bass register would be processed through fixed, and not dynamic processing[/i]

Unless the CV is generated before the frequency is divided?

GordonC wrote:

Sometimes I wonder if people with a surplus of high end gear are really getting the most out of all that fancy kit.

*********************

They are if they think they are, regardless of the opinions of any of the rest of us. Only YOU know the sound that YOU want from YOUR theremin.

When the "garage band" sound became fashionable in Rock & Roll in the 1990's, groups would spend a fortune in the finest and most expensive recording studios in the world, attempting to make those studios sound like some kid's basement rec room. Sophisticated FX chains were devised to make digital recording sound "dirty" and "home made".