of Microprocessors

B
SignalBouting
In the previous two chapters, the sound-synthesizing elements that are part
of a computer-controlled analog synthesizer were studied in detail. First,
voltage-controlled circuits such as oscillators, amplifiers, and filters that do
the actual sound waveform generation and modification were discussed. This
was followed in Chapter 7 by a discussion of interface elements such as DACs
and analog switches that allow the computer to control the analog synthesis
circuits. The final step in the synthesis portion of the system is interconnection
of these synthesis and interface elements into a useful system. Of course,
there are almost as many ways to do this as there are system designers, but an
attempt will be made to group these into three different organizational
philosophies, all of which have been hinted at in previous discussion.
The first organization, which we shall call "Type 1," is really no
organization at all. The analog elements are simply mounted in rows on a
front panel, each independent of the others except for power. The computer
interface elements are likewise grouped together and are also logically independent.
Interconnection is done manually by means of patch cords or pinboards,
just as on a conventional synthesizer. In fact, most systems of this
typ~ incorporate a standard analog synthesizer or a collection of standard
synthesizer modules. Interface elements may be standard multichannel DACs
with nothing more added than a jack panel to accept standard patch cords. In
such a system, the computer automates such tasks as sequencing, generation
of arbitrary envelope shapes, smooth manipulation of several parameters
simultaneously, and controlling polyphony. Note that these are the fllost
difficult tasks to perform on a classic manual synthesizer system. Since
off-the-shelf components can be utilized and the overall organization does not
differ greatly from conventional systems, this approach would be expected to
be the most popular, at least for the near future.
The Type 2 organization is like Type 1 except that the computer is in
complete control of the interconnections among elements as well. In its most
elementary form, it is a Type 1 system with a computer-controlled switching
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