As an experimental thereminist exploring some possibilities on non-pitch-critical theremin music the requirement to play "in tune" does not apply to me, so I have no intention to follow this idea through to a working prototype in order to test the validity of my proposal. Nonetheless I think it has sufficient merit that I would like to share it with the denizens of Theremin World.
I note that the requirement to play in tune is the first major hurdle to many would-be thereminists. Undoubtedly the ideal way to master this skill is with the aid of a theremin tutor who can provide feedback to the theremin student. However, as theremin tutors are a sparse resource, it may be desirable for a student to have a device which does as a tutor would do; provide positive feedback when a note is in tune.
There have been many suggestions as to how this might be accomplished. One is currently being discussed in this forum, based around a visual display. Opinion is divided regarding the efficacy of a visual system. My intuition is that this is not the best approach - the thereminist may be using their eyes for other purposes, for instance to read sheet music or to look at the horizon as an aid to maintaining balance and minimise body motion, or may be completely focussed on hearing the theremin and hence not paying attention to visual stimuli. My intention is not to undermine that proposal - some students may prefer that approach, and when tested it may yet prove to be the superior solution.
Although some theremin tutors may see benefit in a feedback system that provides negative feedback to misplayed notes by means of a powerful electrical current applied to the student, it is more humane to consider a system based on positive audio feedback. I take my inspiration for this from the observation that when I have seen theremin tutors at work, they will often say an encouraging word when the student is in tune.
It is important, in my opinion, that any audio based system should not affect the way the theremin pitch field responds to a player's interaction with it, as this would be at odds with the goal of learning to interact with the theremin without pitch assistance. Therefore I suggest that the feedback should come via a second audio channel: either via the "pitch preview" favoured by some thereminists, or a small loudspeaker placed adjacent to the theremin.
The feedback should mimic the behaviour of a tutor, making a brief, pleasant sound when the pitch of the theremin corresponds to a tone in the tuning system being used, typically A440 12TET. The sound should have a sharp attack and be of short duration - a "ping" - something like a staccato piano note or a glockenspiel note - and be of the same pitch as the note being played to reinforce the desirable pitch in the player's mind.
As vibrato is often a feature of classical theremin playing, I note that the effect of a well played, tight vibrato on the pitch assistant would be to cause it to play a rapid sequence of pings in the pitch of the note being played, and without either of the adjacent notes triggering a ping.
