The world saw the birth of an important and popular electronic instrument when George Beauchamp mated his magnetic pickups to guitars back in the 1930′s, producing the first electric guitar, which he christened the Rickenbacker (then made by his company, Electro String Instrument Corp in Los Angeles). It was an extreme break with tradition and empowered many innovative musicians of the 1930′s-50′s, like Charlie Christian and Les Paul, to break new sonic territory. Many sounds in this new instrument lay latent, however, until the arrival of the 1960′s, when Jimi Hendrix and other contemporary guitarists turned up the volume and started exploring the virtues of distortion and feedback. Together with extensive use of analog electronic effects musicians learned to control these additional degrees of freedom and produce the intensity of modern rock performance. Likewise, from the 60′s and 70′s, other electric guitar musicians, such as Derek Bailey, Fred Frith, and Henry Kaiser, used many kinds of mechanical modifications (employing dental floss, clips, and nearly anything else) to change the sounds of their instruments during improvisational performances.
The first stages in the melding of guitars and synthesizers were experiments with running guitar signals through envelope followers and processing devices such as filters, and ring modulators in the old modular synthesizers. Designers then eagerly assailed the next step in this union, namely extracting the pitch of the guitar, so it can drive an entirely synthesized sound source, and become a true “controller”. This task has proven quite difficult and is still a challenge to do quickly, accurately, and cheaply, even with today’s technology. One of the most heralded early failures in guitar synthesis was the Avitar from the Arp Synthesizer Corporation in Lexington Mass, a device which has been said to provoke the company’s demise.
Starting with the “Probe”, invented in 1976 by the pioneering synthesizer musician and music software developer Roger Powell, keyboard players were able to escape their rigs with portable devices that slung over their sholder like guitars (the right hand played keys and the left hand spun wheels and knobs to articulate the sound). Although this let keyboardists prance around the stage in the style of guitarists (the fusion player Jan Hammer was perhaps the best-known early proponent of this type of interface), it by no means was a guitar controller, and still required keyboard technique.
The late seventies and early eighties saw the widespread adoption of the hexaphonic pickup; a magnetic pickup with one coil for each string, thus producing 6 independent analog outputs, and mounted very close to the strings and bridge to avoid crosstalk. This, together with better pitch extraction circuitry, enabled the design of polyphonic guitar synthesizers such as the 360-Systems devices designed by Bob Easton and collaborators and the well-known Roland GR500 and GR300 series. Although they could be slow and quirky, they gained some degree of acceptance in the community, being adopted by guitar giants such as Pat Metheny and Robert Fripp.
In the mid-80′s, the guitar controller began evolving significantly away from its familiar form, with many devices being developed that weren’t guitars at all, but enabled musicians with guitar technique to gain fast, expressive control over MIDI synthesizers. These avoided pitch tracking all together, and merely detected the playing parameters by directly sensing the fretting finger position and the dynamics of the string being plucked. Perhaps the most famous was the SynthAxe, invented in Great Britain by Bill Aitken. This instrument actually sported two sets of strings; one of which were short lengths across the guitar body used to detect picking, and another set running down the fretboard for determining pitch, as described above. With its faster response, the SynthAxe was adopted by several well-known power jazz guitarists, notably Allan Holdsworth. It was very heavy and expensive, however, thus rapidly spawned a related set of much more affordable controllers, such as the Suzuki XG and Casio DG series, which retained the short plucking strings, but dispensed with the strings down the fretboard, now directly sensing finger pressure there. Only one such device is currently in production, namely the ZTAR from Starr Labs in San Diego, CA. All of these controllers feature several additional means of generating data from the guitar body; e.g., whammy bars (directly producing MIDI events), sliders, buttons, touchpads, joysticks, etc. Much simpler versions of these designs have appeared in toy products (such as the Virtual Guitar from Ascend Inc. in Burlington, MA), some of which are still marketed.
The guitar controllers from Zeta Music in Oakland CA were interesting hybrid approaches of considerable renown that appeared in the late 1980′s. These were actual guitars with a multimodal MIDI interface, culminating in the Mirror 6, which featured a wired fretboard for determining pitch, a capacitive touch detector on each string for determining the expected acoustic damping on strings contacted but not pressing the fretboard, hex pickups for determining amplitude and pitch bend, accelerometers for measuring the instrument’s rigid-body dynamics (e.g., shaking), plus an instrumented whammy bar and other tactile controls. Although they no longer produce guitars (having been bought and subsequently spun off the guitar giant Gibson), Zeta still makes other MIDI string instruments.
In recent years, as signal processing capability has improved, there has been a shift away from the dedicated MIDI guitar controllers described above and back toward retrofits for existing, standard electric guitars that now identify the playing features by running real-time algorithms on the pickup signals. These systems generally consist of a divided hex pickup (still mainly magnetic, although some begin to employ contact piezoelectric transducers, which produce a more robust signal and work with nonmetallic strings) and an interface unit, that runs the pitch and feature extraction software. These controllers, once properly calibrated (often still a nontrivial operation), are said to track quickly and reliably, plus estimate other parameters from the string signals, such as the longitudinal picking position. Some claim to respond quickly enough to enable good performance with a bass guitar, where the string oscillation period is much longer.
Nonetheless, it’s generally accepted that the MIDI standard is inadequate for adequately handling the wealth of data that most acoustic instruments (especially the strings) can produce. While a guitar performance can be somewhat shoehorned into a set of features that fit the 31.25 kbaud, 7-bit MIDI standard, there’s insufficient bandwidth to continually transmit the many channels of detailed articulation these instruments generate. Several solutions have been suggested, such as the currently-dormant ZIPI interface standard, proposed several years ago to supersede MIDI by the CNMAT Center at U.C. Berkeley and Zeta.
From American Innovations in Electronic Musical Instruments
by Joseph A. Paradiso
© 1999 NewMusicBox