Theremin Aptitude and Theremin Parameters
The ability to play this difficult instrument varies a great deal among individuals. I make my observations at many venues, where I bring one or another of my theremins for a demonstration, and invite volunteers to play, the majority of whom had never seen a theremin before. Once in awhile, I am delighted to hear someone play a recognizable melody almost immediately. Usually, these are individuals with practiced ability at one or more traditional instruments. Those familiar with a continuously variable instrument, such as the fretless bass, violin, or trombone, benefit in this regard, since these instrumentalists are already accustomed to correlating hand position with pitch, using aural feedback as the primary basis for pitch control. In this respect, such instruments are more demanding than those with discrete tone intervals (pianos, for instance), since the performer must be constantly aware of, and in rapid, accurate control of pitch on a scale with essentially infinite resolution.
The theremin also poses an additional, unique challenge; the hands do not normally touch any part of the instrument, so steadiness is essential. Less obvious is the requirement for good endurance; it actually takes quite a bit of energy to execute such precise control over the body's position for extended periods. When I first started to play complete compositions in one session, I experienced pain in my hands and arms as a result of maintaining such controlled positions for the duration of a rendition.
Although it is very hard to predict the chance of success for any particular individual at the theremin, I believe that prior experience with musical instruments or as a vocalist, and the ability to persevere through very gradual improvement, are essential. Patience, in this regard, is an essential element in obtaining satisfaction. For many individuals, qualities such as pitch accuracy and adequate phrasing require many years of dedicated practice.
My theremin interests were primarily driven by my vocation as a circuits designer. When I made my first theremins, I found it very challenging to play anything recognizable. I realized that some of my difficulty was due to the instruments' qualities, and not my level of proficiency. So, I concentrated on design improvements to make theremins with optimized responsiveness, addressing parameters such as sensitivity, linearity, stability, harmonic content, and noise. Here, a summary of these parameters provide some insight regarding the characterization of theremins:
The sensing distance of the theremin defines the range of hand distance over which the instrument will respond, the right hand usually for pitch and the left for volume (although these are easily reversible for left-handed players).
The range of response for the pitch and volume are also important parameters. As with many orchestral instruments, it is desirable to obtain at least three octaves, so that melodic leads can be played, especially in the tenor and alto ranges. Taking the concept of sensing distance and range in conjunction, a pitch range of three octaves executable over one foot is reasonable. Most of my designs provide seven octaves for one-and-a-half feet, and while this additional range provides some versatility, the increased sensitivity of response makes pitch control more difficult.
For most purposes, the range of volume provided for one foot of detection distance should be a ratio of at least 100,000:1, or 50 decibels. The relationship of the theremin's volume to distance should conveniently provide the ability for staccato phrasing, when needed. Modern designs can easily achieve a dynamic range of 75 decibels.
Among other important parameter consideration is linearity, which addresses the degree of spatial evenness among the tone intervals. Ideally, the distance from one partial to the next would be equal, as with a piano, so that any particular pitch could be accessed with equivalent distinction. In practice, absolutely perfect linearity is difficult to achieve, although most theremins are sufficient in this respect. Many theremin designs require critical and frequent adjustments to ensure a smooth, logical progression of pitch frequency as the hand is moved to and from the antenna. Typical heterodyne configurations actually might reverse the pitch response at a certain distance, due to the nature of the design. This is generally undesirable, and may be resolved with more intricate circuit schemes.
While these are the most essential theremin parameters, there are also many others which distinguish one instrument from another. Among them, stability is paramount. The theremin offers a formidable design challenge since the physical principle of operation involves the precise measurement of minute differences in capacitance. In electronic terminology, the theremin must be able to respond to a total change of less than 4 picofarads with a resolution of no more than 30 femtofarads. These are very small values of capacitance, and as a result, the measurement process inherent to the instrument is easily compromised by minute instabilities in electronic components, chiefly affected by temperature variations. In practical terms, this means that an instrument's sensitivity and range of response may vary during performance. These variations are often apparent in what is called "offset drift," when the initial knob settings require frequent readjustment during performance. To overcome this problem, careful attention to the circuit design and physical construction of the instrument are essential.
Harmonic content is another consideration when choosing an instrument. This primarily refers to the tonal coloration of the sound. Traditional theremins utilize a technique known as "heterodyning," and the harmonic content which results from this process causes the tone quality of the output to vary with pitch. Especially in the lower octaves, the output tends to be richer in odd-order harmonics, and as the pitch increases, the output becomes more sinusoidal. Breaking with tradition, some elaborate theremin-type instruments incorporate a digital interface for MIDI (musical instrument digital interface) equipped synthesizers, in which the voicing is provided the synthesizer rather than the theremin. I have referred to one such instrument, "The Dimension Beam" infrared gestural controller, in a previous article. Note, however, that the quantization effect created by the MIDI process is not always acceptable, and this process has not become widely accepted among thereminists.
Tonal quality is an important consideration in selecting an instrument, but the criteria is as subjective as choosing colors for a room. My own preference is for a pure sinewave output, although I have constructed theremins with features for harmonic selection as well. Some designs, including the ones described by Leon Theremin in his 1929 United States patent, have one or more tone control knobs.
One other remark regarding tone versatility: Since some compositions benefit from atonal (non-melodic) elements, theremins may also be incorporated to this end, with absolute pitch not a critical factor. This tends to relegate the instrument as more of a "sound effects" device versus a melodic instrument, but this is not necessarily a detraction, since such applications may induce an appreciation for theremin among the public without the need for perfectly-accurate melodic rendition. In this respect, it is nice to have tonal variation available to provide a variety of sounds, in lieu of virtuoso content.
Lastly, the subject of noise gives consideration to two primary factors. First, the susceptibility of an instrument to electromagnetic interference, such as that from a radio station, can cause problems manifested in unwanted audible disruptions. Most units have some sort of tuning provision to selectively eliminate such disturbances. The second type of noise is generally referred to as "hiss," and is largely a function of the design. Another way of expressing this is with the term "signal-to-noise ratio," a term often seen in comparing, for instance, the qualities of compact-disc players, radio receivers, or amplifiers. By definition, this ratio will be at least as large as the volume range, but may exceed this value, which is a benefit.
To my knowledge, there are no widely-used standards for theremins, although it would be nice to see a side-by-side performance comparison for the few commercially-available units. One last thought: Using this instrument with relevance and to the benefit of a composition in "live" situations is not easy. Ambient distractions often make hearing the theremin difficult, and, under these circumstances, the performer no longer has the feedback vital for control. Good, strategically-placed monitors are an asset in this respect, so, if you plan to bring your theremin to concert, be prepared with the right amplifier and monitor speaker for the occasion. In the studio, headphones with a careful blend of the accompaniment is essential.
The Big Briar Etherwave®
The Big Briar "Etherwave®" is very popular among thereminists, and is perhaps the most common theremin used today. It is rather minimal with regard to conveniences, for instance, having no output volume control, no standby ("play/off") switch, and no pilot lamp. The two tone controls, "Waveform" and "Brightness," do not provide much timbre versatility, which, in my opinion, is quite "buzzy" and shrill for all combinations of settings. I would have preferred the inclusion of some timbres which are more sinusoidal in quality.
The instrument's stability for temperature and humidity variation is adequate for most venues, although extreme changes in environment may require recalibration just prior to a performance. The calibration resolution is somewhat limited by single-turn controls, so care must be taken during the adjustment procedure. The instrument has excellent immunity from most types of interference, and also features superb distance-to-pitch linearity, as well as a more-than-adequate pitch sensing distance of at least two-and-a-half feet, when properly calibrated. The pitch response is illustrated below.
Both legato and staccato expression is obtainable by adjusting the "Volume" response control accordingly.
As for ergonomics, the Etherwave® has maintained the traditional approach, featuring a horizontal loop for volume, and vertical monopole for pitch. While the loop makes ergonomic sense, I do not prefer the monopole, since it requires a rather awkward pitch-hand position that may cause strain on the wrist joints.
The volume response, as in most theremins, provides an increase as the hand ascends. While traditional views of the theremin offer some rationale why this is preferable to the "closer-for-louder" design, I personally find it very awkward and unintuitive. One detraction with this design is that the instrument may sound with the performer absent, unless the pitch circuit is precisely nulled. With some difficulty, circuit changes may be made to the instrument to achieve the closer-for-louder response.
The Etherwave® is available as both a kit and a finished unit. The kit contains a pre-assembled circuit board, however, this fact should not minimize the importance of reasonable soldering skills for making the connections between the wiring harness and the panel controls. A soldering iron and solder, not supplied, are needed for this purpose. In addition, some relatively uncommon tools are also recommended, such as appropriate box wrenches for attaching compression fittings to the antennas. This process requires considerable torque, and substituting pliers for the purpose will almost certainly scar the fittings. The kit builder must also assemble the wood cabinet and paint or otherwise finish it. A few materials are not included, such as the epoxy needed to anchor the antenna bushings. In speaking with numerous Etherwave® Theremin builders in recent years, most had no trouble completing their kits by following the well-written directions included. However, I think the modest additional cost of a pre-assembled unit is money well-spent, if the user is more intent on playing theremin than building one.
Arthur Harrison
June 2, 2001
©1997, 2001 by Arthur Harrison