of Microprocessors

9
Organ Keyboard In,terface
After a suitable synthesizer for output and a computer for control have been
found, the final and ultimately most important subsystems are the devices
used to communicate musical ideas to the system. The next three chapters
will discuss devices for original input of musical material as well as equipment
useful for displaying and editing the material. These input techniques
are equally valid for real-time computer-controlled synthesizers and direct
computer synthesis, which will be discussed at length in Section III. Most of
them are fairly standard and were originally developed for computer applications
other than music. One exception is the music keyboard, which is the
subject of this chapter.
Undoubtedly the most popular musical input device will be a standard
organ keyboard. Most new users will prefer it, at least initially, because of
familiarity and because for most reasonably conventional music it is simply
the most efficient method for getting musical data into the computer. Also,
being a mass-produced item, the typical purchase price for a keyboard
mechanism is quite reasonable compared wirh construction from scratch.
Even so, the usual organ keyboard leaves a lot to be desired. For
example, the only "information" avail,tble about a key closure is which key
was struck and for how long. This is just as well, since the typical organ
would not be able to utilize additional information anyway. However, a
music synthesizer, particularly a computer-controlled one, can and should
utilize every bit of information available. To this end, special keyboards that
also sense the speed of key depression, variations in pressure while it is down,
and other variables have been constructed. Fortunately, some of these features
are easily retrofitted to standard keyboards or in some cases may be
merely a function of the interface circuitry used to connect the keyboard to
the system.
One final keyboard characteristic, which piano and organ players usually
take for granted, is polyphony, i.e., simultaneous sounds in response to
simultaneous key closures. Whereas in an organ or piano there is one tone
generator per key, such is not the case in a synthesizer. Furthermore, the
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