Tell us about your experience with Open.Theremin

Posted: 11/15/2013 4:27:41 PM

From: Hillsborough, NC (USA)

Joined: 2/13/2005

Several folks commented on our recent article about the Open.Theremin project, so I thought I'd try moving the conversation into the forums. 

If you've built one, I'm really curious to hear your experience with it.  How do you like the sound, the linearity, the playable range, etc?


Posted: 11/15/2013 5:50:15 PM

From: Northern NJ, USA

Joined: 2/17/2012

No direct experience, but looking at the LC schematic I see the pitch antenna hooked directly to:

1. 100pF to ground

2. The input of a 4069 CMOS gate

Both of these give me pause.  The first because it needlessly limits sensitivity, the second because IMO it is bad engineering practice.

They are heterodyning before detection, which likely limits low end frequency capture resolution.  It wouldn't surprise me if there were significant lags associated with playing it.  One can low pass filter all kinds of sins, but this leads inexorably to slow tracking if you aren't really careful with everything that comes before. 

They are heterodyning because the asthmatic Arduino can't handle fast precision timing, nor does it handle audio generation very well.  So their choice of processor on which to base this project seems suspect.

Godspeed and all to this project, but my main fear is that the perceived limitations of these early semi-digital offerings will close many people's minds entirely to the digital approach.  IMO, digital is the only way to make stable, linear, feature rich Theremins that are relatively inexpensive and easy to manufacture.

Posted: 11/16/2013 4:30:03 PM

From: Scotland

Joined: 9/27/2012

Point of order:

Given the opening question, it is wrong to have the instrument damned by someone who has no hands on experience.

I agree dewster that your knowledge of electronics may give you an insight as to how the instrument would fair theoretically but again, I'll repeat, that it does no good to go rubbishing it without having tried it.

I have an Open Theremin and was considering commenting further on it's operation here but given that anything I say has already been prejudiced by my reply to dewster's premature comment (in my opinion), I will not.

Incidentally, ' main fear is that the perceived limitations of these early semi-digital offerings will close many people's minds entirely to the digital approach.'-dewster

(Bold highlighting is mine)

With this closed midset, where would developement of any inovation go?


Posted: 11/16/2013 4:53:16 PM

From: Hillsborough, NC (USA)

Joined: 2/13/2005

Everyone's opinion is their own... Feel free to speak your mind Roy.  The point of this thread is to get actual feedback on the theremin from people who have experience with it. 

If dewster sees obvious engineering limitations to it, well... that's a perspective I also appreciate because I wouldn't have been able to figure that out myself.  It is an open source project... Feel free to contribute back to it to help improve the design.  I'm also very excited about the prospect of having a low-cost, stable, linear, and good sounding theremin in the market.  Whether that ends up being Open.Theremin or not is yet to be seen.

Posted: 11/16/2013 5:19:15 PM

From: Brooklyn,NY

Joined: 12/1/2009

Roy, if you actually have an OPEN theremin, no one's comments should 'prejudice' yours.  And even if they did,  Dewster knows his sh*t so it is not like listening to some random internet troll's opinion on digital theremins.  Personally,  I want to hear both his opinion and yours...

here mine:      First off... i have no experience with the open theremin other than thru the web, but I gotta say that it look pretty cool.  The hardware looks pretty slick. At best it could offer a really low cost point of entry for those wanting to dip their toes in the therein pool and will probably draw in a lot of hacker/tinker types.     Ultimately tho', as one with experience build theremins and working with arduino,  I suspect that any serious players will eventually want to step up to at least an etherwave standard.  Not necessarily the best analog, but like with synths,  an arduino-based synth is pretty cool and can do some amazing thing, but ultimately cant hold a match to any budget level 'real' synth like a micro korg.

...but lets see what others say.

Posted: 11/16/2013 5:28:45 PM

From: Northern NJ, USA

Joined: 2/17/2012

I realize that I spoke out of turn here and I apologize. 

RoyP, please don't let my uninvited technical criticism of the Open.Theremin dissuade you from relating your experiences with it.

Posted: 11/17/2013 12:20:12 AM

From: Scotland

Joined: 9/27/2012

Hi all,

I let a post get under my skin and had a bit of a rant...apologies.

It's late just now and my neighbours (nice as they are) would not react very well to me firing up my theremin to take sound clips so I'll report in due course.


Posted: 11/17/2013 12:53:06 AM

From: Canada

Joined: 8/1/2008

Excuse my ignorance, but I know absolutely nothing at all about this thing called "Open.Theremin". Is the following video of Rachmaninoff's VOCALISE an example of this device?

Posted: 11/17/2013 2:43:35 AM

From: Northern NJ, USA

Joined: 2/17/2012

"Is the following video of Rachmaninoff's VOCALISE an example of this device?"  - coalport

It seems so.  Is it my old ears, or is there something strange going on starting around 4:00 with the audio in that video?  Like the pitch is catching or the volume is peaking at certain frequencies or something.  It could be YouTube compression I suppose.

Posted: 11/17/2013 11:32:02 PM

From: Scotland

Joined: 9/27/2012

The Open Theremin is an Open source theremin piggy backing onto the Arduino motherboard.
It is programmable via the USB connector on the Arduino and can be powered by the PC/USB connection or an external DC supply.

As explained in the Open Theremin setup instruction guide, the theremin has to be manually calibrated to adjust for specific differences in the user antennae to those suggested.

This is done via a two part calibration process: firstly, the variable capacitor for the tank circuit of the pitch antenna is adjusted so that an audible frequency of 600Hz is achieved. Then after a long depression of a small button, the variable capacitor in the Volume circuit is again adjusted to an output of 600Hz.

Once this has been done, the theremin is auto calibrated for zero beat and maximum distance away from the volume antenna by another shorter depression of the button (3 audio beeps over about 2-3 seconds) signal that this calibration is taking place.

The theremin is now ready to play.

(NB In my experience the theremin is best switched on for around an hour for manual calibration and at least 30 minutes before auto calibration and playing.)

Observations on playing the Open Theremin.

Initially finding the correct playing distance from the instrument was kind of tricky for me since I was used to adjusting the pitch/volume fields manually with potentiometers-relying on a 2-3 second window to get in the ‘playing position’ was strange but after a while it works.

The instrument gives an octave range of just over 5 octaves and this seems to be fixed within the distance chosen at the auto calibrate, ie you can have 5 octaves in an arm’s length to the antenna or 1.5m from the antenna. Irrespective, you will have the full 5 octaves.

My only other theremin doesn’t have such an octave range and so initially playing this instrument felt a wee bit strange.
That said however, now it feels fairly easy to play (not-with-standing the usual difficulties of playing the theremin!) with what feels like a fairly constant linearity (see graph in the photos area).

Up until a few days ago I was playing through a small battery/mains powered Vox amp but have bitten the bullet and bought a Behringer K450FX (I believe that our Thierry has one of these). This amp has an exceptionally neutral response with a good power output and with the Open Theremin played through it two things are immediately revealed: the extended base response of the theremin and at high frequencies, a noise superimposed on the ‘music’ signal. This can be heard (I think) on the audio file ‘Scan UpDown’. Also, under quiescent conditions (volume hand away from the volume antenna at zero beat) a similar but quieter noise can be detected.

It has to be noted that with a lesser amp I had not been aware of these ‘dirt’ signals over the main ‘music’ signal.

After several manual calibrations at several different times I wonder if success in the setup of the instrument is pivotal at this point? It has to be said that it is quite tricky and from experience, how well one cap is adjusted will affect how well the other one can be adjusted: if the first one is maladjusted then adjusting the second one will either be difficult or when adjusted will not have a significant effect on the respective antenna. I have noticed that if the two caps are out of adjustment the octave range will be less and the volume rise/fall will not be smooth but will have the potential of break-up.

Certainly, I have noticed that with a lesser octave range, the noise ‘dirt’ at the high frequencies is less, due I think to the cut-off of octave range before these frequencies are reached.

I have noticed also on the Open Theremin site that a reference has been made to the effect that the program code has been altered in an updated version of the program to reduce noise.

Playing the instrument poses no problem as far as I can see and there is no detectable lag-so far it seems to respond quickly to any movements that I can throw at it.

The sound the instrument produces is determined by a waveform table which can be altered, re-saved and then substituted in the program for the new waveform. I have tried this to varying degrees of success although the waveform which is standard with the program is perfectly acceptable. Two others are available on the Open Theremin site to try.

Also, the CV out has not yet been programmed-to be fair, I have been in contact with Urs Gaudenz, the designer about this and he has said that since the project is a open source, he has left this un programmed so that it may be programmed to suit individual needs and to that end, he has said that he is happy to programme the output if I suggest a voltage range per octave, which I have not done yet.

Sound files are on Soundcloud at

‘Scan UpDown’ is a sweep of the octave range up and down (there is a glitch towards the end which is due to my laptop hard drive not the theremin!)

‘NGL1 and 2’ is part of Neil Gow’s Lament to His Second wife-as always, all bum notes and dodgy glissandos are the fault of the player not the instrument!

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