The TaurEx
The TaurEx is a sensor extension for the electric guitar that tracks motion and reads performance gestures in order to provide wireless, real-time control of computer effects and sampling. Designed and built by Kevin Patton, the interface of the TaurEx allows Patton to control an array of computer effects and processing while playing — including delay, harmonization, granulation, and sampling — with subtle gestures such as hand position and the movement of the guitar neck. There are also force sensors that operate independently and can be assigned to directly control aspects of the computer such as switching between effects scenes or setting the output levels of different processes.
The modified guitar began life as a 1987 Steinberger GM4T with the famous Trans Trem. The active pickups give a variety of sounds, from a strat out-of-phase sound to a fat gibson. None of the sensor modifications have permanently altered the vintage instrument. Indeed, one of the priciples of TaurEx is that it can be fit to any guitar without altering its playability or finish. The headless design was perfect for placing a sensor at the end of the neck.
The TaurEx can be thought of as two independent networks of sensors. One is gathering information about the gestural qualities of how the guitar is being played while the others primarily operate as assignable controllers. There are two two-axis accelerometers: one on the end of the neck of the guitar which follows the motion of the instrument itself. There is one on the first finger of the picking have and is watching pick motion and figer speed. These accelerometers are combined with an infra-red distance sensor and a force sensor on the back of the neck to gather latent and not so latent performance qualities.
The second system of sensors is created with six independent force sensors. There is one on the front to the guitar easily accessible by the thumb. There is a set of five on the left hand cutaway. These can operate independently as a mixer, or they can be routed to directly control processing or sampling.
Sensor conditioning was an important part of getting reliable consitant data. The very first version of TaurEx used the Teleo system to interface with the computer. This proved unsatisfactory. Although Teleo is a great approach to get something working out-of-the-box, certain sensors—especially the accelerometers—needed conditioning. With this version of the TaurEx this is acheived by using rail to rail opamps. Currently this is being housed in a wood enclosure and is held to the strap of the guitar with velcro. The next version will shrink the sensor interface and will attach to the strap with a leather pocket. This all runs at 5 volts and is connected wirelessly to the computer via bluetooth.
Of course any sensor or set of sensors can be turned into a controller. It is especially interesting to play the TaurEx as a large gyro, where balance and tilt control sound synthesis parameters.
Here, using the 'mixer' force sensors.
The TaurEx from the front.
