730 Chapter 20
based on analog techniques and slowly gave way to
digital techniques as this newer technology developed.
Digital techniques came into full flower with the devel-
opment of powerful digital signal processing chips or
DSPs. It now became economically feasible to concen-
trate the functions of filtering, equalization, signal
delay, compression or limiting, and frequency division
or crossover into a single system interposed between the
input console and the power amplifier. This new digital
signal processing unit was given different names by
different manufacturers but was popularly referred to as
a loudspeaker management system. The current trend in
more powerful power amplifier design is to provide the
entire required signal processing function within the
confines of the amplifier chassis itself. In many
instances there is no requirement for an external loud-
speaker management system. These amplifiers usually
accept audio in both analog and digital formats with the
digital format conforming to the AES3 standard. If the
amplifier is to be employed in live sound reinforcement,
a premium is placed on having low latency in the ampli-
fier’s digital signal processing functions. Latencies of
2 μs or less are highly desirable.
20.3.8 Computer-Controlled Power Amplifiers and
Systems
Computers are permeating every field of human
endeavor and audio systems are no exception. Crown
International Electronics in the middle 1980 s pioneered
computer control to the depth of the level of individual
amplifiers. Crown, building on the digital electronics
and programming experience it had acquired in the
development of the TEF analyzer, began designing a
new line of power amplifiers that would be amenable to
both digital control and digital monitoring with the
incorporation of a plug-in digital module. Parallel to the
development of these amplifiers, Crown also developed
the computer interface and communication system
necessary for interaction with these amplifiers. This
work culminated in the Crown IQ system.
The original Crown IQ system was structured on
three levels with microprocessors at each of the levels.
At the uppermost level were the host computer and the
IQ system software. The host computer could be any
computer that had a serial (RS232, RS422, or RS4230)
port. The computer with the installed IQ system soft-
ware acted as a monitoring and control station. At the
intermediate level was the Crown IQ interface that
served as a communication device between the indi-
vidual power amplifiers and the host computer. At the
lowest level were the individual power amplifier plug-in
microprocessor cards that were connected in a daisy
chain by means of a single twisted pair to form a serial
loop to the IQ interface as shown in Fig. 20-42.Communication between the interface and the indi-
vidual amplifiers was at a baud rate of 38,400 so that
the system operation appeared to occur almost in real
time. All of the normally manually controlled functions
of each amplifier could be computer controlled by this
system up to a total of 2000 two-channel power ampli-
fiers. The outstanding feature of this approach,
however, was that the actual operational status of each
amplifier including on-off, input level, output level,
distortion, and safe operating area were constantly
monitored almost in real time. Subsequently, the Crown
system was expanded to include plug-in modules incor-
porating digital signal processing capability in addition
to the original features. This allowed, in addition to the
original monitoring and control features, online
filtering, signal delay, and equalization, all under
computer control.
The modern era of control of sound systems began in
1993 with the step taken by Peavey Electronics Corpo-
ration in the introduction of the MediaMatrix® System
that featured real-time network communication and
control of digital audio signals by Ethernet supported by
a CobraNet® hardware interface. This system allowed
the interconnection, communication between, andFigure 20-42. Basic OCIA pulse width modulator.InterfaceSerial loop, 38,400 baudAmplifier plug-in cardsRS232 or RS422
300–38,400 baud