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Of the Theremin and Futurist Stringed Instrument Making

Sound quality

During the course of my “thereminist” career (albeit more as a builder than a player), I realized one fundamental aspect: the theremin is as alive and full of personality as any acoustic instrument.

But what does a good theremin sound like?
It is not easy to describe the sound of a good theremin in words.
We can say that its inventor described it as an instrument capable of reproducing the tones of bowed instruments or the human voice.
I suggest you listen to the CD The Art of the Theremin made by Clara Rockmore: the higher tones of her theremin (which was built by the inventor himself in the 1930’s) are strikingly similar to those of the well-modulated voice of a soprano, whereas the lower tones are the same as those of a ‘cello.
The RCA theremins traded in the 1930s also have a timbre that is very similar to that of a ‘cello.

The sound of modern theremins is slightly worse than that of their predecessors.
For example, the Etherwave of Big Briar (a company founded by the mythical Robert Moog) has a waveform control knob that allows the creation of sounds ranging from those of bowed instruments or the human voice to more exquisitely “synthetic” sounds, but it lacks the clarity and vivacity of the vintage models. Nevertheless, I think that the Etherwave is a good starting point for anyone who wants to begin practicing the art of the theremin.

Lydia Kavina’s theremin (built in England by the engineer Anthony Henk) is an excellent instrument with a practically infinite range and optimal linearity: in brief, a professional instrument. But even this lacks something in terms of quality as the generated sound still has an over-synthetic flavor. Nevertheless, it certainly has its own personality and, when you listen to it, you have no doubt that you are listening to the theremin of Lydia Kavina.

At a cost of $3,500, the latest Big Briar instrument (called Ethervox) is highly professional and its MIDI controls offer all of the benefits of MIDI technology: digitally generated sounds, the implementation of movement-controlled musical sequences, automatic pitch control and the possibility of using external MIDI modules.
I have never tried it but I am told that it optimally produces the sounds of classical theremins as well as those driven by its MIDI interface.

The other theremins on the market include the PAIA Theremax which, although being cheap and entertaining, does not guarantee adequate sound performances. Nevertheless, once again, I would like to underline that it could be a good starting point for aspiring thereminists.

In my opinion, the most important aspect of a good theremin is a constant evolution of pitch throughout the entire range of tones. However, an analysis of the waveform of a properly constructed theremin shows that, as a result of the intrinsic distortion of the beat generation, it varies as the pitch changes: this gives the instrument a richness of tone and expressiveness that is difficult to reach using electronic instruments with conventional synthesis.

Images of wave forms
Images of waveforms.

If we add the fact that the intensity of the sound is freely controlled in a dedicated manner by the movements of one hand, we can see that its expressive potential can be compared with that of a conventional instrument.

The primary requisite of a good theremin is therefore that the quality of the sound: it must be the most natural (or the least electronic) possible.
When we rank theremins on the basis of their sounds, we find that the best have tubes based circuits. I have already said the mixer is the heart of the instrument insofar as it is responsible for what we hear. Both Theremin and RCA used a tetrode, a type of tube that has two control grids positioned inside the electron flow developed between the anode and cathode. The beat is made available by connecting the signals transmitted from the two oscillators to the control grids on the transformer of the anode charge.

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