Is Open.Theremin.UNO worth it? Cannot it be drastically simplified?

Posted: 3/9/2015 9:08:42 PM
xtheremin8

From: züriCH

Joined: 3/15/2014

100 points for that one! the theremini only makes sense as a controller with nice midi features. but as a instrument in the sense of a theremin...no sir. therefore i simply love urs's design etc...

frankly, the wavefront i ordered just passed swiss customs! i'm a bit excited...

Posted: 3/9/2015 10:10:01 PM
Thierry

From: Colmar, France

Joined: 12/31/2007

A wavefront? Ouch!

Posted: 3/9/2015 10:45:01 PM
xtheremin8

From: züriCH

Joined: 3/15/2014

felt that. ;-) i know it's a bit a controversial thing when it comes to wavefronts...specially a rather old thread about "pumping" made me curious. there's that ouch too, and me wonders what they talked there... i barely know the instrument by experience, limited to some days of a diy festival, and i liked the playability and the sound very much. true, the suitcase looks a bit odd. feel free to deepen your concerns. even by p.m. if you like.

Posted: 3/9/2015 10:58:27 PM
3.14

From: Buenos Aires, Argentina

Joined: 9/14/2008

Wonderful consequences of this topic!

Talking about CV...

I was thinking if it would be feasible to use, instead of a variable oscillator heterodyning with a fixed one, just a "load sensing" over a fixed oscillator (just like the EM/EW does for the volume antenna).

[Note for Etherwave newcomers (if there is any...): The EM/EW theremin, for the volume antenna, uses a fixed (though slightly tunable) oscillator, and the inductors + antenna capacitance "load" the circuit with an impedance that varies according to hand distance (i.e. the capacitante changes, thus the resonant frequency of the series circuit changes). When properly tunned, the current drain varies with hand distance, thus the voltage drop accross the inductor changes. This voltage drop drives the VCA.]

The proposal here is to use this technique and let the voltage drop to drive a VCO.

Then the resulting voltage can simply be acquired with a fast and precise enough ADC to drive the wave generator.

If the fixed oscillator frequency/generation is uP-controlled, it can be automatically tunned.

I seem to remember that this approach has been discussed before (when Fred was designing a theremin) but cannot find where. If not, can we discuss it?

 

Posted: 3/13/2015 8:33:41 AM
gaudi

From: Switzerland (CH)

Joined: 8/6/2010

Thank you Thierry for this great contribution and everyone for this constructive thread. I think the approach by Thierry to mathematically model classic theremin instruments adds a lot to better understand the physics of the instrument and holds a lot of potential for future developments.

Posted: 3/13/2015 8:41:09 AM
gaudi

From: Switzerland (CH)

Joined: 8/6/2010

Gaudi, I think the limitations of the Arduino are really holding you back at this point.  There are lots of processor project boards out there now, you might even find one with integrated audio DAC.

The open.theremin shield should fit on a Freesceale Board frdm-k64f with 32bit M4 ARM Core. This would probably allow real time sound generation based on mathematical models. Who want's to give it a try? (As Thierry noted the 3.3V supply must be considered.)

Posted: 1/13/2016 3:39:51 PM
Seawolf2913

Joined: 1/13/2016

Sorry for posting so late to this thread.

Gaudi-  I'll be purchasing an uno board soon.  (Just have to inform my bank that they should clear an international purchase.)  Have you ever come across the Teensy boards?  https://www.pjrc.com/teensy/teensy31.html  72MHz Cortex-M4 processor that can be programmed in the arduino environment.  Even if you are doing ATMEL specific things in your code,  it could be a good starting point.

I know that any periodic waveform in the sum of sine and cosine functions, but some people are just visual.  Inkscape is an SVG drawing program that can be scripted in python.  Let me look into digitizing a bezier curve in inkscape and outputting a text file that can be included in an arduino project. 

Posted: 1/16/2016 12:40:22 PM
Thierry

From: Colmar, France

Joined: 12/31/2007

The Teensy 3.x processors are definitively worth a look. But one can't simply rely on the internal 12bit DAC if one wants an audio quality which satisfies sensitive musician's ears and a "professional" dynamic range. Either you'll have to do lots of post-DAC analog filtering or you make a pre-DAC effort to upsample the signal with a digital polyphase FIR filter to virtually increase the resolution.

Seawolf2913, there exists already a visual wave form generator tool for the open.theremin.uno here.

For those who are interested in using a mathematical model to emulate the classic "Moog" wave shaping used in the Series 91, Ethervox and all Etherwave (including Pro) models, there is an article here.

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