Is linearity affected by surroundings / environment?

Posted: 6/17/2009 2:53:26 PM

From: Seattle, WA

Joined: 2/6/2009

Quick question here: does anyone know if linearity is significantly affected by the environment around the Theremin? I have a Etherwave Pro that I've been practicing on in a nearly empty room for a few weeks... recently we got a couple pieces of furniture nearby and I'm noticing the linearity isn't as good as I thought it was. It could just be me getting more aware of the nuances of the instrument, as I'm still an early beginner. But if it turns out that the furniture is degrading linearity I'll consider putting my furniture to Craigslist :)
Posted: 6/17/2009 4:03:51 PM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as . ...................................

Joined: 12/7/2007

Linearity is affected by the environment - any conductive objects change the background coupling to earth, and depending on the position and degree of coupling, can distort the E-field significantly.

As to whether this is the cause of the non-linearity you now notice, it would probably be a good idea to test the Theremin in an empty room before you do anything drastic!

My comments above are based on observations I have made, mostly in a highly conductive, cramped lab environment.. I found that the frequency / distance relationship changed dramatically as I repositioned my prototype/s.. This has caused me many problems - I had expected that the linearisation requirements would be only marginally affected by the environment - but I found that (under extreme conditions) not only could one distort the curve, but one can actually get 'discontinuities' in the curve - response may be linear for a given distance, then go 'bumpy' and then go back to nearly linear. I have experimented with environments quite extensively, as I am developing electronic linearisation, and need the system to cater for worst case 'reasonable' extremes (exactly what "reasonable" means is a bit difficult to determine! :)

As I say, my conditions are extreme - most are not the sort of conditions one would normally get.. But yes, it certainly is possible for objects to affect the Theremins linearity.

Fred Mundell
Fundamental Designs Ltd.
Electronics Consultant.
<- See Profile Image for Email.
Designer of Theremins and other alternative electronic music controllers and instruments.
Posted: 6/17/2009 4:17:49 PM
RS Theremin

From: 60 mi. N of San Diego CA

Joined: 2/15/2005

Good response Fred, sometimes I think the theremins have a mind/spirit of their own!

I can’t speak to the E-Pro directly because it may respond differently but here is my quick answer: Environment affects the pitch “note spread” the most; while less influenced is the pitch note linearity which ideally should stretch out or compress equally. A theremin set up in an open area is affected the most by temperature and humidity changes. The proximity of furniture, even a metal frame, should have an undetectable influence beyond four feet because it sets on the lowest side of the pitch field, in other words near the ground.

After making many observations on this particular subject, I only know of three near perfect linear theremin designs. That would be the EtherVox, E-Pro and my heterodyne scratch built RS Illusion theremin using a LC tuned pitch antenna.

My interpretation of perfect linearity in a pitch field is where the octaves are the same width from the outside 20” right up to next to the antenna. Example: if the octave of A1 is 4” in width then the octave of A5 would be 4” in width next to the antenna. There would be “no” bunching up of the high notes in the last 3”. Perfect linearity will give you a crisp vibrato on the high notes and surprisingly the very “lowest” notes.

I purchased an EtherWave Standard to study its linearity and found it to be disappointing, though it is the theremin I recommend for first time players to purchase because of its durability and resale value.


Posted: 6/17/2009 7:14:31 PM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as . ...................................

Joined: 12/7/2007

[i]"sometimes I think the theremins have a mind/spirit of their own!"[/i]

LOL! .. Christopher, although it goes completely against my scientific "grain" - I am inclined to agree with you!

[i]"I can’t speak to the E-Pro directly" [/i] .. I know this is not exactly what you meant.. but I found this thought of talking directly with a Theremin highly amusing! - I wonder what they would say (or sing?) back us ? ;-)

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