of Microprocessors

284 MUSICAL ApPLICATIONS OF MICROPROCESSORS
DIGITAL I/O BUS
MODULE
N
2-CHANNEL AUDIO BUS
CHANNEL
I
CHANNEL
2
Fig. 3-5. Fixed-patched system
packages. While not a one-evening project, an automatic patching system
can certainly be practical when compared with the rest of the system.
Fixed-Patched Computer-Controlled System
An instrument-oriented synthesizer is really a radical departure from
the function-oriented synthesizer discussed up to this point. The system
"bu;lding blocks" are now entire sounds or "voices" rather than low-level
signal-processing functions. Thus, a typical synthesis setup should require
fewer modules and interconnections as well as being easier to understand.
The price paid for this simplicity is flexibility, since many decisions have
been made by the module designer rather than the user. For clarity we will
refer to the usual voltage-controlled functions such as veos, VCAs, etc., as
"function modules" and the others as "voice modules."
An analogy to logic ICs is easily drawn. The typical function modules
are like fundamental logic elements such as gates, flip-flops, and singleshots.
Voice modules, on the other hand, are more like MSI circuits such as
decoders, counters, multiplexors, and read-only memories. In modern logic
design, one often uses these sophisticated MSI functions to perform mundane