Pitch Drifting .. .. ..

[i]"this is the first time time I have ever heard that a thereminist can be improperly grounded..." - Coalport [/i]

LOL! ;-) - Is there such a thing as a properly grounded thereminist?

joking aside.. I am not surprised that this aspect of the dynamics of capacitive coupling is not common knowledge amongst thereminists.. These are invisible and complex forces, and the majority of people only have a vague idea about what capacitance is.. it is complex enough with just 2 'plates' to think about, but a thereminist is equivalent to a third 'floating' isolated 'plate' between the antenna 'plates' and the grounded 'plates' - if one tried to compute your effective contribution to ground capacitance while playing, you would be somewhat distracted! ;-)

But here is the bottom line..

The stronger the "invariable" coupling of the players body to ground, the less important variable capacitive coupling (via capacitive coupling of the body, arms, hands etc to grounded objects - such as the theremin itself or cables etc) will become.

If the primary coupling of the thereminist to ground is via anything which moves, then this movement will change the pitch/volume almost as much as if it was a movement directly related to the antenna/s.

I did not realize the importance of variable ground coupling until I did my post-mortem on my Epsilon multi-dimensional controller, and discovered this to be a fairly major factor in its poor operation..

I will now go off on one of my long-winded theses.. LOL! ;-)

There are 4 primary sources of ground coupling for the thereminist – these are:

C1.) coupling via feet / body to the floor and other large grounded objects such as walls, and to cables etc. This is usually quite constant and stable, and quite large.

C2.) coupling of the thereminists body to the theremin, amplifier, cables etc – If the thereminist does not move his/her body, this is constant – moving towards these objects will increase the ground coupling, moving away will reduce it.

C3.) Coupling of the pitch hand / arm to the ground components of the theremin – This variable grounding does not cause a problem, as it is part of the thereminists pitch control loop, and will be corrected automatically, and go unnoticed.

C4.) Coupling of the volume hand / arm to the ground components of the theremin – This variable grounding CAN cause a problem, as it is not part of the thereminists pitch control loop.

The extent to which C4 influences the players grounding (and therefore influences pitch) is dependent on C1 (and C2).. If C1 and C2 are low, the effect will be greater.


Examples:

C1 = 100pF, C4 varies between 0.01pf and 0.1pf.
Players capacitance to ground will vary between 100.1 and 100.01pF so the ground capacitance will vary by about 0.1% as a result of movement of the volume arm..

Fortunately this capacitance will be in series with the capacitance between the pitch antenna and hand, which reduces the effect greatly – so if, for example, this capacitance is 0.2pf, then the capacitance to ground ‘seen’ by the pitch antenna will vary from 0.199601196 to 0.199600838 pf or 0.000179%

Now, for C1 = 10pF, C4 varies between 0.01pf and 0.1pf. with pitch antenna – hand at 0.2pf:

Players capacitance to ground will vary between 10.1 and 10.01pF so the ground capacitance will vary by about 1% as a result of movement of the volume arm..

capacitance to ground ‘seen’ by the pitch antenna will vary from 0.196116505 to 0.196082272 pf or 0.017455% which is significant!

The greater the direct (unchanging) coupling of the player to ground, the less will be the influence of other (variable) couplings to ground.

Fred.

ps.. in answer to Carports question: "I'm curious as to whether one could play a theremin while falling through the sky?"

The answer is that the C2 (coupling between theremin and [falling] therem

I apologize for taking this thread off topic.

In the [b]heterodyne[/b] theremin pitch field hand capacitance is not the main fundamental affecting the pitch range. One method to verify this is to reach toward the pitch antenna with the palm of your playing hand parallel to the antenna. Bring your other hand forward and place it behind your forward hand, now slide the back hand to the side without going past the forward hand. Interestingly the pitch will remain unchanged even though the surface area capacitance with both hands side by side should have doubled.

It is the “distance” between your forward finger/knuckle and the antenna that has the most controlling effect. This is why a well trained Thereminist can change the shape of their hand without significantly changing the pitch.

If you want to know more… (http://www.oldtemecula.com/theremin/observations.html)
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Hi Christopher,

you say:

[i]"In the heterodyne theremin pitch field hand capacitance is not the main fundamental affecting the pitch range. One method to verify this is to reach toward the pitch antenna with the palm of your playing hand parallel to the antenna. Bring your other hand forward and place it behind your forward hand, now slide the back hand to the side without going past the forward hand. Interestingly the pitch will remain unchanged even though the surface area capacitance with both hands side by side should have doubled."[/i]

of particular importance is the statement "the surface area capacitance with both hands side by side should have doubled."

This is innacurate - it would only apply if the thickness of the antenna directly parrallel to the hands had the same area as the hands - which it certainly doesnt have except perhaps for horizontal plate antennas. On average, the effective thickness of a rod antenna is less than 20mm - angular capacitive coupling between the hands and the antenna does occur, but its contribution to total capacitive coupling is far less than that proposed in your experiment.

[b]Added->[/b] The angular components become more significant the further the hand/s is/are from the antenna (the further from the antenna, the narrower the angles from the antenna required to encompass the hands completely - closer to the antenna, wider angles are required.. The wider the angles, the less significant an increase in horizontal width of the hand/s becomes.. This is why it is possible to change the 'shape' of the hand without altering the pitch, and why tiny movements of the most significant fingers (those parrallel to the antennas 'plate' area) can has far greater effect on pitch than movement of fingers which are not directly parrallel to the antenna.[b]<-[/b]

As to the mechanism of pitch control - I disagree with your hypothesis almost entirely.. Yes, there are some [b]extremely minor[/b] contributions from other effects, but the bulk of theremin control is a purely capacitive effect.

[b]Added->[/b] The reason for my disagreement is that no other mechanism is required to explain theremin operation - capacitance is a full and mathematically provable mechanism.. When one has a simple mechanism which can be proved, one does not normally find that a more complex mechanism which cannot be proved is the correct one - variation on Occams Razor (http://www.desy.de/user/projects/Physics/General/occam.html) I suppose..

If one has a spreadsheet on which one has distances increasing from 5cm to say 1M in 5cm steps, and you have constants for antenna dimensions and hand area, one can then generate a table of capacitances for each distance.. You can then use these capacitances as values to feed computation of frequency for LC and RC circuits.. Do this, and you will get EXACTLY what one gets from a real circuit.. Ok - because of the complexity of the relationship between the equalizing inductor and the LC oscillator, I did not include this inductor in my spreadsheet or test circuits.. but the fact that the results tallied perfectly shows me that changing capacitance is what determines the frequency.

When adding an equalizing inductance to a simulation, and then building the circuit and testing the real circuit against the simulation, the results tally ... The simulator only has changing capacitance, which, again, proves that change in capacitance is the only mechanism required to achieve control of theremin pitch.. no other explanation is needed, as far as I can see. [b]<-[/b]

I do understand why you have concluded that some mechanism other than capacitance is in operation.. The changes in capacitance when ones hand if further from the antenna than about 30cm are extremely tiny, and the inclusion of a well tuned equalizing inductor has a 'majical' effect on sensitivity of a LC VFO..

However, it IS possible to obtain the same sensitivit

Fred: thank you for your response. Your posts at the wee hours of your morning tell me you have a manic curiosity of exploring theremin principles and possibilities.

Do not dismiss so quickly the theory I present. A perfectly linear pitch field can be very stable and is an advantage for the new Thereminist, it is easily achievable. It is as much a part of theremin fundamental theory as is heterodyning.

You have a gift which few could pursue and it is my hope you continue to dabble in your theremin research. I wish you the best in health.

Christopher
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Hi Christopher, thanks for your kind wishes.

Yeah - the "wee hours" are when I am at my best.. not quite so manic during the day! ;-)

It is nice to have a functioning brain again though! - for a few months, the act of thinking was a real challenge - just wanted to curl up and let everything pass me bye.

It is not so much "theremin principles and possibilities" which inspires me - it is exploration of almost anything I have any doubts about which drives me I think.. I do not believe that it is possible to absolutely prove anything as being "true", but I do believe it possible to prove things to be untrue, and eliminate these. You theory has not been proved untrue, and my (the conventional) explanation that change in capacitance is what controls sound from a theremin cannot be proved to be the only mechanism.. I keep an open mind .. All I can say with certainty is that control of a theremin by change in capacitance alone fully explains the theremins operation, and no other mechanism seems to be required.

Whilst on the subject of exploration - I need to explain that some of my observations were not the result of playing with theremins..

I was commissioned (prior to starting on theremins) to examine all the electronics based "free energy" devices which had been disclosed on the www and elsewhere, and to build / test / evaluate them - I had a large budget, but was not free to tell anyone what I was doing, so could not discuss the projects with anyone. I had one year when I worked on nothing else, and several years where about 50% of my time was spent building and testing (mostly) incredibly stupid ideas.

I never expected to find anything which worked, but did everything I could to find one.. The antenna experiments were part of these explorations.

I found one possible source of "free" energy - This was based on Floyd Sweet's VTA.. And this was an example of how an incredibly complex unscientific theory had been concocted to explain something where a simple scientific mechanism explained everything.. The "free" energy was provided by converting thermal energy to electrical energy via some mechanism which, due to incompetence or deliberate sabotage by a "free energy expert" has now been lost.

I am happy to explore "pseudo-science" when the scientific method has been exhausted - But pseudo-science, IMHO, is dangerous - I believe there are discoveries which have been lost simply because some bogus nonsensical explanation has beed concocted, and those hearing this nonsense walk away without exploring the actual phenomena for themselves.

my advice to anyone who discovers something 'strange' is to present what they have discovered WITHOUT trying to explain the mechanism - unless they are sure their hypothesis is rational and does not contradict the fundamental laws.. It MAY be that some physical fundamental will need to be re-evaluated.. But this is extremely unlikely - and if one presents a hypothesis which goes against these laws, no-one will bother examining the phenomena.

Further hijacking of this thread has been avoided by Christopher starting This new thread (http://www.thereminworld.com/forum.asp?cmd=p&T=5055&F=3) where this discussion is continued. Thanks Christopher.

Fred.