of Microprocessors

6
BasicAnalogModules
Probably the most important idea in the history of analog music synthesis is
that of a modular synthesizer. Prior to the conception and implementation of
this idea by Robert Moog, numerous special-purpose synthesizers and, according
to their designers, "general-purpose" synthesizers were built and
used. Music synthesis, however, is such a large and complex problem that
even the most ambitious general-purpose machines had serious
shortcomings. The major shortcomings were in the structure of the machines,
not the capability of the various oscillators, amplifiers, and filters that did
the work.
In a modular system, the structure is largely unspecified. The user
defines the structure appropriate to the requirements at the time and interconnects
the available modules to realize that structure. When that requirement
has passed, the modules are readily reconfigured to meet the next
requirement. The idea is roughly akin to the concept of movable type in
printing.
Analog System Standards
There must be some consistency among the modules, however, in order
to insure compatibility when they are connected. Before continuing, a few
system-wide "standards" that typically apply to a broad range of commercial
analog modules will be outlined. Standard power supply voltages are + 15 V,
+ 5 V, and -15 V with respect to system ground. The 5 V supply is used by
digital logic elements in the system and the ± 15 V is used by analog
circuits, such as operational amplifiers. All supplies are tightly regulated,
usually to better than 1%, although some high-frequency noise can be
expected on +5. The standard power supply voltages are generated and regulated
at a central location and distributed to all of the modules in the system.
Other voltages used by some digital and analog ICs such as + 12 V, - 5 V,
and -12 V are conveniently derived from the standard voltages with IC
voltage regulators (some of which are less than 50 cents each) or zener diodes
or even resistive voltage dividers.
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