of Microprocessors

SIGNAL ROUTING 277
I MUSIC
KEYS
+ •
JOYSTICK
---
SOFTWARE
SYSTEM
I
COMPUTER
----.Jl
MULTICHANNEL
DAC
r--
VCO VCO I VCA VCF
MATRIX ~,---J
C
I
ONTROl
>
I
LL='-
/"
E
COMPUTER-CONTROllED
SWITCHING MATRIX
Fig. 8-2. Type 2 automatically patched system
distortion of the control voltage contours. Most multiplexed DACs, however,
provide sufficient filtering in the channel sample-and-holds themselves.
Automatically Patched
Computer-Controlled System
An automatically patched system in its elementary form is a Type 1
system with the jacks and patch cords replaced by an electronic switching
matrix that is under the computer's control. Such a system is represented in
Fig. 8-2 but in practice the switching matrix may be organized differently
from the two-dimensional matrix shown. Comments about the synthesizer
and the computer made earlier are just as valid in a-Type 2 system. Therefore,
let us proceed directly to a discussion of the switching matrix.
The simplest type of patching matrix, at least conceptually, is the
straight rectangular array of single-pole switches as in the drawing. All
subsystem outputs, including the DACs, drive the columns, and all of the
subsystem inputs are connected to rows. The final synthesizer output is
considered as an input to a speaker subsystem. The number ofswitches in the