TherAsynth - New product under development - What do YOU want?

Posted: 2/3/2008 4:38:42 PM

From: Colmar, France

Joined: 12/31/2007

I agree with GordonC that linearity must not be the holy grail.

If you take a violin string, the first octave takes half of its length, the second octave only a fourth of its length and the third one no more than an eighth, which makes it very hard to play more than 2 octaves on one string. That's why a violin has four strings and most music for it is limited to 3 1/2 octaves plus perhaps some special effects such as flageolet tones.

A very good trained professional human voice reaches 2 1/2 to maximum 3 octaves. A flute and a clarinet have 3 octaves, a recorder only 2.

So I conclude for me and I agree with Thomas Grillo, that 5 to 6 playable octaves would be fine, so that one would have the double range of most "natural" instruments.

"Playable" doesn't mean for me "absolute linearity" but that I should be able to get at least a quint from making a fist to extend all fingers (which is 7,5cm or 3 inches with my small hands) at the lower end of range and at most an octave at the higher end, similar to the "feeling" when playing a string instrument.
Posted: 2/3/2008 4:44:22 PM

From: Croxley Green, Hertfordshire, UK

Joined: 10/5/2005

Thomas - it just occurred to me - Lego is made of ABS, and, astonishingly, there are instructions for building a Lego Theremin on the 'net, albeit a rather primitive photo-theremin...

(Shame the link to the video doesn't work. Or maybe a blessing - I bet it was just dreadful.)

Thierry - the impression I got was that field size and pitch range are independently variable - if you want one octave over 30cm, that's fine, you can have it; if you want ten octaves over 10cm, you could have that too. Or any other combination, within certain limits. I think it's the limits that Fred is asking about - what is the biggest and smallest field you would want, what is the smallest and largest pitch range you would want.
Posted: 2/3/2008 5:25:03 PM

From: Toledo, Ohio United States of America

Joined: 2/22/2006

"Also - I am also thinking about supplying the unit as a kit - this would consist of 2 fully assembled (and encapsulated to stop anyone coppying them) sensors, and 3 assembled and tested circuit boards each having 7 potentiometers mounted on them, and a few wired switches and sockets etc, and a drilled aluminium panel - The kit builder would provide their own cabinet which will need to be completely screened internally with aluminium or copper foil or tape."

I would love a kit version as I have built many a wooden box to house my own electronic projects, but I think that a optional box should be offered to facilitate those without my dubious box making skills, as it were.
Good Luck, and God Speed!

Has Moog offered to buy you out yet? HA!

Posted: 2/3/2008 8:08:30 PM
Jeff S

From: N.E. Ohio

Joined: 2/14/2005

"Linearity is not necessarily the holy grail."

I believe you mean to say it is not that important to YOU.

We already have plenty of functional theremins available that fulfill the other requirements set forth. They provide a frequency range of 5, 6, or more octaves and a "wide" field for making circles in the air.

I do see how the relatively narrow "cone" of a capacitive sensor could be a problem for some people. It could be a problem for everyone if it is too narrow.

The importance of linearity depends largely on what you want to use the theremin for. Personally, I feel it is of great importance. I play using hand shapes. My hand is one fixed length, so linearity from the upper to lower octaves is important to me.

I'm skeptical that Lydia Kavina plays with a nonlinear field by preference. Only she knows for sure. I'm sure there are times when it may come in handy for some people.

Since there are, as yet, no theremins with a truly linear field, we've all had to adjust to playing in a nonlinear field, whether we like it or not. Since that is the case, there are other factors that also influence our choice of instruments.

My personal requirements are 4 1/2 octaves in about 20" (50cm) with the ability to adjust up or down from there.
Posted: 2/3/2008 8:22:44 PM
Jeff S

From: N.E. Ohio

Joined: 2/14/2005

Now....if you could dial in the frequency range (octaves) and the field range (distance) independently, that would be something!

On a side note, I've been kicking around ideas for theremin cabinet design for a few years now. I think I've come up with some interesting and viable ideas, although I haven't sat down and drawn them all out in detail yet.

Naturally, innovative ideas are not going to be inexpensive to execute, so they would be of little value for a modestly priced model.

Posted: 2/3/2008 11:19:32 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 am astounded (and a little bit frightened) by the level of interest.. So before I say anything else, I must warn you all that I do not yet have a functional prototype of the complete unit – I have a few functional ‘breadboards’ and a large number of nearly functional breadboards, and a huge number of fully functional simulations – I hope to have the first fully functional prototype in a few months (but unless I limit the time I spend on this board a bit, that could stretch to 6 months.. LOL!)
All information given here, and in preceding posts, is correct to the best of my knowledge – But this is still a work-in-progress, and specifications are likely to change (hopefully for the better) and I may have got some things wrong.


[b][i] Thomas Grillo : FredM, revisiting your statement about the fields being conical, and directional. Does this mean that if I'm playing in a croweded venue, that someone can just walk right up to the instrument from the side oposite the player, and not affect the instrument?[/i][/b]

[b] Yes! [/b] – or at least the effect would be greatly reduced – I have not done full tests on the shape or fringing of the detection field, but, for example, I can place the sensor on my knee and play it, and minor body movement is not detected unless I lean forward into the sensing field.

[b] Sensing field linearity[/b]
The edge detection zone of the field does not have a linear relationship – the linear relationship only applies when the hand is fully inside the field, and is moved towards / away from the sensor / antenna. I am not sure what the edge field relationship is – but it is ‘soft’ and probably square law

[b] Sensing field distance and octave coverage[/b]
The distance from the antenna over which the instrument can be played is determined exclusively by the physics of the sensor and the environment. The following is an extremely simplified and incomplete description of how the sensor works:
When the sensor is turned on, it starts monitoring the capacitance, and continues this updating every 10ms, if it finds a capacitance lower than what it has seen before, it logs this value and recalibrates itself, and if it finds capacitance higher than what it has seen before, it does the same. At any instant, the sensor has a) The largest capacitance it has seen b) the smallest capacitance it has seen c) the present capacitance.
These values are mathematically processed, and resultant capacitive range is linearized and split into 65000 ‘points’ which are effectively 65000 linearly spaced distances over the range of detected capacitances, and the instantaneous capacitance detected every 10ms is mapped onto its point and the corresponding voltage is output.
The output voltage ALWAYS spans 0 to 10V from the minimum to maximum detected capacitance. The sensor also computes the ‘unreliability zone’ at the low capacitance end (the area where change in capacitance is extremely small, and computation results can jitter) and adjusts itself to eliminate this zone .. This is an area I am working on at the moment – and it impacts greatly on the distance of the sensing field – If this zone is large, it will reduce the sensing distance significantly.. I THINK that my present sensor, with this zone removed, has a distance range of about 30cm – But I will need to work more on this and related sensor issues such as capacitive plate size.

The player will need to move their hand over the full detection range (from closest to the antenna to furthest from the antenna) once to get the sensor calibrated – thereafter it will take care of itself, and the linear sensing field will be set. The distance of this field will be determined primarily by the size of the capacitive plate (antenna) in the sensor, and also by the players capacitive coupling to ground (but this is usually extremely large by comparison, and not too significant – particularly as my TherAsynt
Posted: 2/4/2008 12:17:12 AM

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

[b] Thomas Grillo: A couple of other items on the wish list would be the ability to make the volume antenna very sensative so as to allow staccatas, while still being able to provide nice cracendo, and eminuendo control.

Switchable Pitch Preview through one earbud jack would be nice so as to be able to switch preview off at will when just practicing in private, and one might not need or desire preview going at that particular time. [/b]

Ok – Time to let another cat out the bag.. Preview has puzzled me intensely since I started looking at these kind of instruments – I have an idea which is so simple I cannot understand why I have never seen it done… it can be done with ANY Theremin, extremely simply..

Connect a frequency counter (or ideally a tuner which displays musical notation) to the oscillator (actually, to the output from the modulator after the HF filter, in the case of a conventional heterodyning Theremin) before the control amplifier (VCA) and one can see the pitch which will emerge when one allows it through.. One can buy a low cost multimeter with frequency display covering the audio range for about £15

I intend to include a single 7 segment display showing AbCdEFg with decimal point indicating sharp, and another showing 0 to 9 indicating octave – No more earbuds!

With regard to volume sensitivity – TherAsynth can assign the output from this antenna to both VCA and VCF and both gain and polarity can be altered – I can make the gain as high as required – Would maximum sensitivity = 1cm be high enough? Minimum sensitivity will always equal the full detection field (say 30cm)… One could have the VCF on low sensitivity, allowing the VCF to be played with the VCA fully open. (VCF does not need to be in-circuit at all by the way – I suppose I am a synthesist first, and perhaps wrongly think in these terms more than in terms of classical Theremin playing)
Posted: 2/4/2008 12:44:45 AM

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

[b] DECAY + ‘STRUM’ [/b]

I have included a couple of unusual controls to TherAsynth – these are a ‘Decay’ knob and a ‘Normal/Delta’ switch.. With the switch in Normal position, and Decay set to minimum, the volume antenna acts as per conventional Theremin.. Increasing the decay causes the volume (control voltage to the VCA) to track the volume antenna when volume is being increased, but to decay at the rate set, to any lower volume level. This allows a player to simulate other instruments which have a fast attack and slow decay – they simply ‘blat’ the antenna and move their hand quickly away from the sensing field.

With the switch in ‘delta’ position, the [b]rate of change[/b] of movement detected by the volume antenna is converted to a voltage – the decay control sets decay (effectively like the length of time a violin string will resonate after being bowed – the rate of change being the energy at which it is bowed) In this mode, one must continuously move ones hand over (towards + away from) the volume antenna to get an output.
Posted: 2/4/2008 6:13:32 AM

From: Croxley Green, Hertfordshire, UK

Joined: 10/5/2005

With regard to linearity, not my place to presume upon Ms Kavina's motives, but having had the privilege of Lydia and George's company during the build up to Hands Off, I would characterise them both as level headed people with a clear view of what they want, and the tVox Tour was built to her specifications. We also note that it is also the weapon of choice for those of her students (including Barbara Buchholz) who were around while it was in production.

From the description of Fred's proposed instrument I suspect linear/logarithmic could be a user selectable option, as it is just a software mapping.

What is always desirable is field stability. Whatever the field does, it should be invariant and predictable. Again it has been suggested that this is a feature of the instrument under discussion.

(A thought - could the pitch field extend across a surface marked with a faux keyboard, like an electro-theremin (aka Tannerin) or faux frets for those of a logarithmic bent?)

With regard to pitch preview, there are certainly more players that favour an audible preview than a visual one (the only player I know to use a visual preview is Barbara Buchholz, and I seem to recall that Clara Rockmore's instrument had a light that illuminated when she played A0, mind you, I also read that it's primary function was to allow her theremin to double as an oversized tuning fork for an orchestra) although, as Kevin Kissinger recently pointed out in another thread, an easy to read visual preview does have some useful applications and can be used in conjunction with an audible preview.

The reason, incidentally, Fred, for favouring an audio preview is that a theremin player's attention is very highly focussed on the sound - pitch is maintained by a tight ear/hand coordination. Perhaps you have come across the phenomenon of "theremin face" - the blank, "lights on but nobody home" look that many players have whilst playing - this is a result of focus shifting from the eyes to the ears. I imagine that many players would be startled to realise that a polka-dot elephant had been watching them play and they didn't even notice.

With regard to extra functionality. Your design sounds very modular - separating the functions of distance location and tone generation, for example. My preference would be for a very straight-forward device with all the design effort going into making it a practical, solid working tool to start with. (For me the tVox epitomises that - easy to carry, easy to set up, ultra-reliable, and genuinely useful niceties only - examples being two audio outs - one for the player's monitor amp, one for the mixing desk/P.A. - and auto-calibration for the volume loop (press a button, put your hand where max volume should be and wait a couple of seconds.) Once I have good, basic instrument, then it would be neat to be able to pick and choose from a range of add-ons to add the extra functionality I want.

With regard to the surprising levels of interest show, especially considering that you're at a very early stage in development; this is not the first hybrid design we have come across recently, but you are the first bravehardy enough to discuss it openly on the TW forums.

Here are a few links regarding recent developments in the UK, Germany and Russia... (first posting on page)

[i]Would maximum sensitivity = 1cm be high enough? Minimum sensitivity will always equal the full detection field (say 30cm)[/i]

Is that upside-down? The conventional arrangement is that raising the hand raises the volume, lowering the hand lowers the volume. A minority of players prefer the other way around, and it is common in theremins on display in museums, for practical reasons.

Posted: 2/4/2008 8:06:24 AM

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

Is that upside-down? The conventional arrangement is that raising the hand raises the volume, lowering the hand lowers the volume. A minority of players prefer the other way around, and it is common in theremins on display in museums, for practical reasons.

Sorry - what I meant was would a 1cm travel from max volume (0db) to min volume (-88db) be sensitive enough - all I am doing is changing the amplification applied to the CV - the CV goes from 0 to 10V over (say)30cm - so amplifying this by 30 will give 0 to 10V over 1cm

All the CVs can be adjusted from +VE max, through 0, to -Ve max .. Ie, it is possible to have volume increase as one removes ones hand from the antenna, or to have this reversed.. The reason for this is again rooted in synthesis.. I am (as much as possible) building a standard set of circuit modules - I want to be able to control amplitudes and harmonics freely (and sometimes perversely) so may want the VCF to track the volume antenna inversely to how the VCA tracks the volume antenna.
It is the VCF's which really make this a synth - and allow harmonics to be controlled from both pitch and volume antennas, so enabling accurate simulation of both classic Theremins and other 'meatier' lead insrtruments like the Mini Moog - in a nutshell - the VCF can increase OR decrease harmonic content when pitch is increased / decreased, and this control can be added to volume antenna signsal which also can increase or decrease harmonic content as volume is increased or decreased.. and the span of both of these can be dissimilar, so any number of harmonic variations or exotic effects can be achieved (a VCF can also self oscillate, adding another tone source - so 3 oscillators can play simultaniously, producing a chord which will track the pitch antenna)

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