1452 Chapter 38
made this sort of processor the overwhelming favorite
of consultants and contractors worldwide.
Systems installed today still use analog micro-
phones and microphone preamps, and in some cases
analog mixing consoles, the outputs of which are fed to
the virtual sound processor. Likewise, the outputs of the
virtual sound processors are usually connected in the
analog domain to conventional power amplifiers, which
are then wired to loudspeakers. Thus considerable
portions of the total sound system remain outside the
scope of the virtual sound processor. There is a better
way, however, that was first used by the U.S. Senate
sound system installed in 1994, and continued in the
new system installed in 2006.
Each senator has his or her own small microphone
equipped with a tiny Kevlar reinforced cord. Suitable
microphones with direct digital outputs were not avail-
able. The cord is managed by a Servoreeler Systems
servo controlled reeler located in the senator’s desk,
under the control of the virtual system. No slip rings are
used, and the far end of the cord is directly connected to
the preamp, also located in the desk. The analog gain of
the preamp is also under the control of the virtual
system. The output of the preamp drives an A/D
converter, which is connected to a DSP processor, and
also located in the desk. The initial audio and control
processing is done in the desk. Audio, control signals,
and power are carried on a single cable between the
desk and the central processor portion of the virtual
sound system. The central processor performs all the
mix-minus processing, and many of the auxiliary func-
tions. Outputs from the central processor go back over
the same cable to the desk, where further processing is
done, still under the control of the virtual system, and
the power amplifiers and speakers are driven.
What is special about this system is that not only is
the central processing done in a virtual sound processor,
but the processing associated with the microphones and
loudspeakers is also part of the virtual system. The
entire system consisting of redundant central proces-
sors, over 100 desk units, custom operator’s console,
and several displays, is all part of a single integrated
virtual sound system. All of the DSP processing,
including both central processors, and the over 100
remote processors in the desks, is loaded with their
operating code and controlled, from a single common
virtual sound system program. Even the microphone
reelers, which are a servo controlled electromechanical
subsystem, and the analog microphone preamps, are
under the control of the virtual sound system. There are
no unnecessary A/D and D/A conversions, and the
longest analog interconnection is the microphone cable.
Sound is converted from analog into digital at the end of
the microphone cable, and remains in the digital domain
until it is in the loudspeaker enclosure. The U.S. Senate
sound systems, both the original of 1994 and the
updated 2006 system, can be considered to be proto-
types for the virtual sound systems of the future.38.4 Virtual Sound Systems38.4.1 MicrophonesThe virtual sound system of the future will be pro-
grammed and controlled through a single unified user
interface program. It will have no analog interconnections.
Microphones will have a direct digital output, and
receive power and control signals through the micro-
phone cable. The Audio Engineering Society Standards
Committee has issued the AES-42-2006 Standard
defining a digital interface for microphones. The digital
audio transmission scheme used is based on the AES3
Standard, but adds digital phantom power, microphone
control, and synchronization features. The microphones
can phase-lock their internal sampling clocks to that of
the equipment to which they are connected. The first
microphones meeting this standard contain conventional
analog microphone elements with conversion into the
digital domain done inside of the microphone body. In
the future, we may see microphones that produce digital
signals directly out of the microphone element. In either
case, these new smart digital microphones can be
controlled by the virtual system to which they are
connected. Some of these microphones will even allow
their directional patterns to be changed, and in some
cases to be steered toward the sound sources under the
control of the virtual sound system. By dynamically
adjusting the pickup pattern and direction of each of the
microphones, the sound system may adaptively opti-
mize its performance.
Microphone arrays will enhance the control of the
directional patterns and aiming of microphones. Micro-
phone arrays consist of from three to hundreds of
microphone elements whose outputs are processed to
produce one or more virtual microphones with control-
lable directional patterns and orientation. They will
have the ability to produce narrow pickup patterns if so
desired, which can be aimed dynamically at the desired
sound source. If the sound source moves, the pickup
pattern can also move to follow the sound source.
Because of this capability, array microphones will be
capable of picking up intelligible sound from a greater
distance than traditional microphones. This will allow