Virtual Systems 1445Loudspeaker processors are another common
example of integrated digital subsystems. Such devices
might include input-level adjustment, compression,
signal delay, equalization, and crossover functions. Each
crossover output might include further signal delay,
equalization, level adjustment, and limiting. Often
manufacturers provide standard settings for their loud-
speakers using these processors, thus optimizing the
performance of the loudspeaker to a degree not other-
wise possible, while allowing one universal processor to
be used for many different products in their line.
The limitation of such products is that their internal
configuration is fixed, and therefore the possible applica-
tions are limited to those the manufacturer anticipated.
One solution is the one pioneered by Dave Harrison
in his analog console designs. In an age when most
recording consoles were custom built, and provided just
the features and signal flow capabilities requested by
the studio owner, David designed a console with so
many features, and such flexible signal routing, that it
could meet the needs of a very wide range of users. Any
one user may not need any but a small subset of the
available features. A few users might have requested
additional features if they were having a custom console
manufactured. Through innovative engineering, David
was able to design this console in such a way that it
could be mass produced for significantly less cost than
the more limited custom consoles it replaced.
Applying this same concept to integrated digital
devices led to devices designed with signal processing
and routing capabilities well beyond the average user’s
requirements. This, of course, made such a device
capable of application to more situations than a more
limited device would have been.
38.2.3.7 Configurable Devices
The next significant advance in integrated digital signal
processing was the user configurable device. In such a
device, the basic configuration of the signal flow and
routing remains constant, or the user can select from one
of several different possible configurations. Next, the
user can select the specific signal processing that takes
place in each of the processing blocks in the selected con-
figuration, within certain constraints.
This sort of device is fine for situations where the
basic functions needed are limited, but some degree of
customization to suit the job is required. The TOA
Dacsys II was an early example of this sort of system,
and was available in two in by two out and two in by
four out versions, Fig. 38-3.
For example, a complex processor for a loudspeaker
might have multiple inputs optimized for different types
of audio inputs. There might be a speech input that is
bandlimited to just the speech frequency range, equal-
ized for speech intelligibility, and has moderate
compression. There might be a background music input
that has a wider frequency range, music-oriented equal-
ization, and heavy compression. There might be a full
range music input which has music equalization, and no
compression.
The input processing chain for each will have a level
control and a high pass filter for subsonic reduction or
speech bandwidth reduction. The speech input chain
might next have a low pass filter to reduce the
high-frequency range. All three inputs will then have
multiband parametric equalizers to tailor their
frequency response. The speech and background music
inputs would then have compressors for dynamic range
control. The three input processing chains would end in
a mixer that would combine them into a single mixed
signal to drive the output processing chains.
Such a system might have three outputs, one for the
low frequencies, one for the midfrequencies, and one
for the high frequencies. The low-frequency processing
chain will have a high-pass filter set to eliminate
frequencies below the reproduction range of the woofer.
Next, it would have a low-pass filter to set the crossoverFigure 38-3. TOA Dacsys II digital audio processors (center and right). TOA’s second generation digital audio processor
(the SAORI was the first), it had a Windows-based control program, which allowed a limited amount of internal reconfigura-
tion of the signal flow. On the lower left is a digitally controlled analog matrix mixer, which could be controlled with the
same program.