of Microprocessors

712 MUSICAL ApPLICATIONS OF MICROPROCESSORS
Hybrid Keyboard Synthesizers
In the mass market, the term "synthesizer" really means "keyboard
synthesizer." As that name implies, the primary operator interface device is a
piano-like keyboard, usually with 61 keys (five octaves), although 73 or even
88 for high-end and 49 for budget units are also seen. The keyboard is
virtually always completely conventional. The keys are a standard size and
shape and move a standard distance in response to a standard force. Many
high-end units even attempt to simulate the inertia of piano keys by using
weights, throw-bars, or other mechanisms. As in the computer market, any
significant departure from such a "standard" keyboard meets vigorous
customer resistance.
Besides the keyboard, the operator typically has two hand-operated
variable controls available. These are frequently called "wheels" because of
their smooth action and have a spring return to their center position.
Usually, one of them is patched into all of the instrument's oscillators so that
the whole instrument can be shifted flat or sharp and is called the pitch wheel
or pitch bender. The other is available to be patched into any sound variable
and is usually called the modulation wheel. Added to these hand-operated
performance controls are one or two foot pedals that plug into jacks on the
instrument. Usually, one is a simple on-off switch to control note sustain,
while the other may be a variable control for volume or some other parameter.
The most visible distinction among keyboard synthesizers is in their
control or programming panel. Every manufacturer and model is intentionally
different, much like video games. Since most keyboard synthesizers are
microprocessor-controlled internally, common digital devices such as pushbutton
switches, thumbwheel switches, calculator keypads, light-emitting
diodes (lEDs), and numeric displays are commonly used. It is not unusual for
a front panel to be 8-10 inches high and as wide as the keyboard, with much
of that area covered by dozens of individual buttons and lights and several
different displays, button groups, and a keypad or two. Recent units have
used alphanumeric and even low-resolution graphics liquid crystal and
fluorescent displays and membrane buttons.
Readers with a computer background may question the wisdom of
using all of this "stuff' when a small alphanumeric keyboard and CRT
display would be much neater and more general. Part of the answer is
historical, since current control panel practice is an evolution of simple early
panels in which a CRT did not make sense. Also, CRTs are not always as
rugged as might be desired for a portable live performance instrument.
Studio-oriented keyboard synthesizers do exist that make use of a CRT
display or in some cases a separate conventional CRT terminal. In the future,
liquid crystal display panels may be able to approach CRT resolution at a
competitive cost and thus negate these objections.
One very cost-effective method of implementing the sound generator in
a keyboard synthesizer is to use hybrid circuitry. "Hybrid" here means a