NEW UK DESIGNED & BUILT THEREMIN with volume loop & pitch rod etc

"Fred- so you you're saying that this interaction is caused by the loop (or wire running to it) being  physically too close to a ground point , like a wire or trace, in   the theremin circuit?   Or did you mean externally, but nearby ( like a huge radiator or house plumbing)?" - Chobbs

The interaction is caused by ground at the theremin - As in, its circuit board mainly, and in the case of a metal theremin enclosure (which I am looking at using) the ground of this enclosure (and the enclosure will couple to the theremins ground - It needs to be actually connected for stability, but if it isnt it will still couple capacitively to the circuit). Other "local" ground sources include leads etc.

Again, as I labouriously detailed above, the effect will be more pronounced if the players other couplings to ground is poor..

The closeness of the loop to the theremins ground is not, in itself, the problem.. It is that when the players hand gets closer to the loop, it also couples more strongly to the theremins ground.. This results in the players capacitive coupling to ground increasing, and this increase is also seen by the pitch antenna..

If this is a problem, then moving the volume antennas operating point (or at least the distance at which the theremin is silent) further from the antenna, so that pitch change is silenced before it becomes bothersome, is the easy fix..

The other (best) fix is to ensure really good ground coupling to the player through other paths rather than directly (via changing hand capacitive coupling) to the theremin.. A conductive mat under the player, connected directly to the theremins ground, or an ECG pad... Greater and consistant player to ground coupling is the cure for many ills..

Alas though, not always easy - Easy in a studio, but move your theremin to some venue where there arent any pipes or cables under the floor, or for whatever reason grounding is poor, and your linear theremin can behave like a Gakken and your volume antenna affect the pitch...

Ok, most people wont notice! ;-) And I am probably being pedantic.. And perhaps real thereminists are automatically compensating for volume-pitch shif and dont even know that they are doing this.. But I do know it occurs.. And I think it occurs on every theremin to some degree, and can be noticable (and to me, annoying) if one sets the volume "null" point too close to the antenna -

I noticed it first when trying to learn to play the damn instrument - Trying to use the volume antenna.. I found that even trying to maintain a constant pitch while trying to master volume control was impossible - At first I thought I must be moving my pitch hand in "sympathy" with my volume hand, because the pitch always increased as I reduced the volume..

But I then found that moving the volume null point up by 20cm rather than having it set about 5cm from the volume antenna (I was nearly touching the antenna to silence it) got rid of the problem.. I actually prefered the null positioned close to the antenna though - It is (to me) easier to determine visually where the null point is when operated like this.

Having the loop (or volume rod) moved 30cm horizontally away from the theremin completely removes the "problem".. I have a capacitively "neutral" (actively shielded)  lead between the theremin and the volume sensing section, so this neither reacts to the hand nor gives any ground effect.

I was still not able to usefully use the volume and pitch together - And have realised that my major problem, which pales all the others into utter insignificance, is that playing the pitch takes 110% of my, very personal computer's processing power - I am waiting for an implantable co-processor to appear (at an affordable price- Complete with an auxillary PSU to reduce circulatory load) before I will have any thought of attempting to master the theremin... And if the co-processor is any good, it will probably convince me not to waste any more time on this stupid instrument! ;-)

Fred.

The horizontal volume antenna as normally implemented seems problematic in the first place.  To quickly silence a note the player has to move their hand quickly yet carefully towards it (all the while concentrating like a demon on the pitch hand).  I would think this situation might produce a certain anxiety in the player, as hitting the volume antenna could make the pitch antenna wobble, or cause the whole unit to topple and crash to the floor.

Standard disclaimer about my lack of playing experience, but the Moog Melodia arrangement of moving one's hand vertically near a vertical plate on the end makes much more sense to me, though knowing how it works might produce unconscious left / right movements of the player's left hand that then influence the pitch.

Ideally IMO the left hand could pass completely through whatever is physically manifesting the volume field, with the field itself possessing little or no left / right bias to it's sensitivity.  Maybe a horseshoe shaped antenna placed horizontally and with the open end facing the player?  Maybe stick an LED beam in there for super quick envelope events in addition to the usual gradual capacitive functionality.

"Ideally IMO the left hand could pass completely through whatever is physically manifesting the volume field" - Dewster

Interesting idea.. A true "loop" but invisible (or visible but permeable) - Anyone into holograms ?

I think an accurate invisible loop could be implemented using two focussed capacitive sensors ("antennas") built into the side of the theremin, with their field focusses overlapping, so one could derive a differential capacitance and from this produce a volume control voltage.. One could have the volume hand a long way (horizontally) from the theremin with such a scheme (say 40cm) , and still get good vertical control..I think this would be really nice - vertical resolution on this kind of sensor arrangement is unafected (after analogue [or I suppose digital] processing) by horizontal movement - and one can also derive horizontal movement as a seperate voltage.

One could also probably use quite a few different kinds of sensors to implement this sort of function.. Perhaps 2 ultrasonic sensors being used alternately to TX and RX,  - one sensor pointing horizontally from the side of the theremin, the other also from the side, but angled upwards - using the delay time combined with triangulation the reflective objects position on X and Y could be determined.

But (at least the capacitive method) is not simple - certainly too complex for a basic function like volume control.. This kind of system is similar to (could use the same basic technology) what I have been chasing for years - A 3d capacitive field joystick.. My technology is too complex and expensive at this time to bring to market.. When I get the cost / complexity down, it will probably be worth putting on the market for use with synthesis and vocal formant control (and theremins, but I doubt that many thereminists will be interested - they have enough to do keeping the pitch, without diversifying to undertake complex tasks with their volume hand such as shifting vocal formants to get the theremin to sing, or controlling filter sweeps and resonance) - but a basic 3d JS will cost more than a reasonable theremin.

Also, I think those who want a conventional loop - well, they want a loop! ... And I think Thierry's reaction to the "Invisible loop inside the control unit" is understandable - It puzzled me at first - but I think there is something intuitive about having something solid with reasonable surface area (whether a loop or a control panel or, like the Melodia, an unseen plate on one side in the theremin)..

I think the idea of a "fake loop" suggested by AIK is the best I have seen so far..

I would love to take the "volume in the control panel" approach, with an extension arm for the pitch antenna (and may yet go this route - Just to get Thierry to jump over his shadow on a Terpistone, LOL ;-) as this approach is probably the easiest and cheapest to implement.. But I am really unhappy with the idea of a pitch arm - even a short one.. And to get adequate spacing the pitch antenna needs, IMO, to be at least 50cm away from whatever acts as a volume antenna.. That is a lot of "wobble leverage".

Hell - I take this all too seriously! ;-) .... Looking at how some recent rubbish has been praised, I can see that theremin enthusiasts mostly dont have a clue - that even quite advanced thereminists wouldnt even notice the effects of their antenna wobbling, and in many cases the antenna wobble would probably improve the performance!

Why cant I just shut up and ride the gravy train ? LOL .. Ok, "train" is something of a stretch.. perhaps a small Hornby loco..

Fred.

Why cant I just shut up and ride the gravy train? LOL . OK, "train" is something of a stretch. Perhaps a small Hornby loco?

Fred.

Ah Fred.

Meals for the single man....................well puppy anyway!

http://www.google.co.uk/imgres?q=gravy+train&hl=en&biw=1366&bih=601&tbm=isch&tbnid=qbv5tLumjHNm2M:&imgrefurl=http://www.wag.com/dog/p/gravy-train-strips-in-gravy-with-turkey-24x132-oz-116976&docid=xz2H4GZLQd5mSM&imgurl=http://c1.wag.com/images/products/p/dmf/dmf-038_1z.jpg&w=1131&h=1600&ei=BTlnUbLRJa6A0AWN6oHACA&zoom=1&iact=hc&vpx=1057&vpy=179&dur=187&hovh=267&hovw=189&tx=100&ty=112&page=2&tbnh=148&tbnw=104&start=22&ndsp=31&ved=1t:429,r:28,s:0,i:175

Hey Chris..

Down in the editor toolbar, there are some useful toys..

If you highlight some text , you will see that two greyed out tools, one looking like an 8 on its side, the other is this same symbol xed oyr..

The "8 on its side" is the link tool - With text selected (highlighted) click on this.. In this you can simply paste your link, and end up with somethingb like This Link - But this doesnt work because its copied from the link you pasted above which is unreadable and probably incorrect because it doesnt work! - because it is too long and one cannot see or grab all of it!   Edit >> It does work! But HOW??? Its an incomplete URL! ..... Oh.. Looks like some redundant data tacked to the end of the URL is ignored... You were just lucky! ;-)

The other tools are [green thing that looks like a cross between a tree and a LCD monitor] = Click on this, paste link to an image, image appears on page!

And the big red button with a white opamp inside it (I think you have used this - but for the benefit of those who havent.. ;-) to insert You-Tube links

So, alas, I have no idea what http://www.google.co.uk/imgres?q=gravy+train&hl=en&biw=1366&bih=601&tbm=isch&tbnid=qbv5tLumjHNm2M:&imgrefurl=http://www.wag.com/dog/p/gravy-train-strips-in-gravy-with-turkey-24x132-oz-116976&docid=xz2H4GZLQd5mSM&imgurl=http://c1.wag.com/images/products/p/dmf/dmf-038_1z.jpg&w=1131&h=1600&ei=BTlnUbLRJa6A0AWN6oHACA&zoom=1&iact=hc&vpx=1057&vpy=179&dur=187&

Is about!  ;-)

Oh, one other tip... If you paste a link, its always a good idea to test this link from your posting.. If you can use your posting to get it, then others are likely to be able to... But if you cant.. ;-)

Fred.

PS.. Well, STONE ME! That damn link I pasted actually worked! How?  Has TW now inheretid the idiosyncracities of the theremin? ? ?

Ok, the link is:

http://c1.wag.com/images/products/p/dmf/dmf-038_1z.jpg

or:

The Link is <-

Or..

This......  8-(    (reduced X and Y by 50%, and its still 100% too big! ;-)

 Ok - I have now removed the image I pasted here.. Chris copied my posting and one such vile image on a page is more than enough! ;-)

Not sure if, in this context, turkey strips in gravy constitutes spam.. LOL ;-)

No Jason!  Really! Theyr'e not paying me to advertise puppy food on TW ! .. Its ChrisC, He's the one to blame!  ... And just because we are both in the UK and live about 10 miles frome each other orll less, well - pure coincidence!!

Ok, the link is:

http://c1.wag.com/images/products/p/dmf/dmf-038_1z.jpg

or:

The Link is <-

Or..

This......  8-(

 Ah, it's alright if the sideways eight is available to you. It used to be, but greyed out for me now. Since the boss used my laptop and it's now on Mozilla FireFox that attachment link is no longer highlighted anymore.

I just highlight the text via left click then right click to see the "open Attachment" & it'll link OK.

Aw, Cmon Chris ! ;-)

Are you trying to get us busted ?

Meals for the single man....................

You know, I think I might just find pot-noodles or spam a treat if I was faced with that stuff..

And one can probably get a healthy vegetable meal for less than the price of a tin of that stuff.. A few potatoes, tub of Lidl cottage cheese, and some veg, one chopped chilli ... Less than the cost of a tin of dog food!

Fred wrote: "Looking at how some recent rubbish has been praised, I can see that theremin enthusiasts mostly dont have a clue"

If you mean me, you're right - my dilettante grasp of electronics is woeful. But I am mindful of having spent a while hanging out with guys in the safety critical process control business. I would get very frustrated at the quality of computer software and hardware, except I understand that while "right first time" is possible, a computer that is nearly 100% reliable is not something I want - it would use a processor that is more than twenty years old (by which time there is a good chance that all the bugs in it have been found and documented), be capable of only a few well defined tasks (probability of bugs increases exponentially with complexity) and outrageously expensive (the cost of thorough debugging is prohibitive.)

So yeah, I tend to be delighted with things even when I am aware of their shortcomings. Like the saying "The best camera is the one you have."

"...a computer that is nearly 100% reliable is not something I want - it would use a processor that is more than twenty years old (by which time there is a good chance that all the bugs in it have been found and documented), be capable of only a few well defined tasks (probability of bugs increases exponentially with complexity) and outrageously expensive (the cost of thorough debugging is prohibitive.)"  - GordonC

Processors tend to be horridly complex even (particularly?) when they don't have to be.  Just add SW and you've got a huge shaky state machine, threatening to topple over at any moment.  IMO, almost everything that can be pushed off and done in software should be, leaving only very basic functionality in a small, sturdy, robust core.  Internal state should be kept to an absolute minimum to facilitate interrupt handling and other context switching.  Any pipelining should be super simple with no stalls or special cases.  Adhering to these principles, I believe it is possible to make useful, practical designs that are easy to verify and implement, and perhaps more importantly that are also conceptually manageable (i.e. fit in one's head with room to spare).

I long for the day when the older architectures (Intel in particular) are way behind us, and system memory is non-volatile, non-cached, and fabricated on the same die as the processor.