of Microprocessors

76 MUSICAL ApPLICATIONS OF MICROPROCESSORS
Finally, the modules of a modern voltage-controlled synthesizer offer
good accuracy in the relationship between a control voltage and the value of
the sound r )rametee being controlled. Thus, two modules with the same
control input can be expected to produce nearly identical results. Although it
is relatively simple to design and produce devices that respond to control
voltages, designing one that accurately and consistently responds to them is
considerably more difficult. Even so, accuracy is one characteristic that could
benefit from improvement.
MECHANICAL
INPUTS
60'
~b
...
,
"-
,
~~c:]
MECHANICAL
OUTPUTS
MODULE
CONT
ROL{
} CONTROL
INPUTS
OUTPUTS
..
SIGNAL { }SIGNAL
INPU TS
OUTPUTS
Fig. 3-1. General voltage-controlled module
Typical Module Characteristics
In examining these points more closely, let's look first at the general
characteristics of a typical module such as diagrammed in Fig. 3-1. This
module has three classes of inputs and three classes ofoutputs. It is rare that a
single module would actually have all six classes of input!output (I/O), but it
is possible.
A mechanical input is a parameter that is physically supplied by the user.
Examples are the positions of knobs, levers, the amount of pressure on a
plate, the state of switches, or other nonelectronic inputs to the system.
There may be none, one, or several such inputs on a single module. In the
case of knobs or levers, two are often used to precisely control one variable: a
coarse adjustment and a fine adjustment. Switches usually set particular
operating modes and may have several positions each. With the exception of
transducer modules such as keyboards) the mechanical inputs are usually set
up ahead of time and then changed only infrequently during the actual
production of sound. Thus, except for transducers, mechanical controls
influence operating parameters that stay relatively constant.
Mechanical outputs are less common and consist of lights, meters,
speaker cones, and similar indications to the user. Except for speakers,
mechanical outputs are just user aids and do not directly participate in the
synthesis process.