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 instruments. He quickly saw that such an instrument would need an unusually versatile keyboard, or control surface. He imagined a two-dimensional control surface that would generate tones whose pitch corresponded to finger position in one axis, and whose tone quality, or timbre, corresponded to finger position in the other axis. A second such control surface on the same instrument could be used by the other hand to control loudness and vibrato. As he thought about it, he realized that he had never heard of such a control. He began thinking how it might be implemented and soon had devised the basic scheme of the Trazor.

When video games with two-axis paddle control appeared, it was immediately obvious that the Trazor was a "natural" for games. Since the market for games was rapidly growing at that time, development of the Trazor was undertaken with this market as the target.

Peptek, Inc. is active in several innovative areas, but is not a product developer. Reston Consulting Group, Inc. is a group with an exceptional record in new product development, so the two firms decided to team up on the hardware development of the Trazor.

In its present state of development the Trazor is a relatively simple device that is readily manufactured. The technical problems of developing it may therefore seem trivial. We found some of them far from trivial.

The knottiest problem was producing a phase field in the control surface that is linear in both axes. We immediately ran into difficulty just trying to produce an electric field that can be varied in each axis independently and is uniform at all points in the surface. We started with a square sheet of material of uniform resistivity. How do you couple signals to the square? You can place conductive electrodes along two opposite edges, apply a potential difference to them, and produce a uniform field between them with its gradient normal to the electrodes. But if you add two more electrodes and try to rotate the gradient to any other angle, a potential difference would have to be established along the first two conducting electrodes for a uniform field to exist. So you try another approach and consider combining the signals you want to apply to the two axes, using four summing amplifiers to give the four algebraic sums of the two signals. You consider applying these four resultant signals to the corners of the square. But the resistance seen by these signals will vary inversely as the square of the distance from the corners, producing a changing gradient that approaches infinity at the corners.

Fabrication of a satisfactory control surface at a reasonable cost was also a problem. We took our problem to several manufacturers of resistive materials, and together we have worked out production techniques that will bring the price down to a reasonable level in quantity production.

Patent applications have been made covering various aspects of the Trazor and its fabrication.

The Trazor can be used in a second mode of operation in addition to the obvious X and Y position control. The position of the point touched on the Trazor can be translated into polar coordinates and used to control the velocity and direction of a game feature. For most applications it is useful to set one or more thresholds,