of Microprocessors

320 MUSICAL ApPLICATIONS OF MICROPROCESSORS
the time of Bach when keyboard instruments really started to be used
extensively. In the past, all kinds of alternate keyboard arrangements have
been proposed to solve this problem including keys that move in more than
one dimension. Although actually building the mechanics of such keyboards
was not too difficult, only recently has electronic and microprocessor
technology made it possible to. translate each mechanical motion into a
variation of a particular sound parameter. Velocity and pressure sensing are
simple refinements that go a long way toward offering a live-keyboard player
the control over dynamics taken for granted by players of nonkeyboard
instruments.
One recent example of a multidimensional keyboard is design work
being done by Robert Moog, inventor and popularizer of the modular analog
synthesizer. The keyboard "keys" are actually just printed patterns on a
plastic sheet overlay. The keys are pressure sensitive but do not actually
move. The innovation is that the keyboard controller not only knows which
key or keys are being pressed and how hard, but also where on the key surface
in X and Y dimensions. Each key, in effect, becomes a tiny graphic digitizer
pad. These three variables plus the key number can then be patched to
control any three sound parameters desired on an individual, per key basis.
The device is inherently inexpensive and can be extremely effective for those
willing to relearn their keyboard technique. In fact, it is probably most
attractive to instrument players without keyboard experience.
Another group doing similar work is Key Concepts. Their Notebender
keyboard looks, acts, and plays like a high-quality conventional
keyboard (Fig. 9-13). However, each key has the ability to independently
slide forward (toward the player) and backward Y4 inch on a frictionless rocker
mechanism with a spring return to center. The only visible clue to this action
is an undercut notch on the black keys to prevent interference with the white
keys. A special friction surface allows the player to move the keys without
finger slippage. Besides this new key "displacement" variable, the keyboard
uses a highly uniform velocity and pressure-sensing technique that does not
rely on switch contacts or conductive rubber pads. As the name implies, the
displacement variable is usually patched to modify the pitch of the note that
key is playing. By means of panel controls right on the keyboard, the bend
direction, range, and programmed nonlinearities in the transfer function (to
aid in bending the pitch by specific amounts such as half-steps) can be
selected and controlled. A 68000 microprocessor is used to control the
keyboard and process information from its sensors. At the current stage of
development, the Notebender keyboard is handmade to very high-quality
standards and is therefore quite expensive. The sensing technology, however,
is inexpensive for the level of precision achieved so costs should come down
when production volume increases.