1454 Chapter 38
the spatial reproduction. In another application, the
same loudspeaker could aim direct sound at the audi-
ence, while simultaneously aiming ambient effects
toward other portions of the room.
Control feedback from the virtual sound system will
allow automatic modification of the loudspeaker
coverage pattern as environmental conditions change.
Such changes might include audience size and location,
ambient noise, temperature, and wind speed and direc-
tion. Integration of DSP processing will also allow other
useful functions to be moved into the loudspeaker
cabinet. These will include source signal selection and
mixing, delay, equalization, compression, limiting and
driver protection, and ambient level compensation. The
programming and control of the DSP processing will be
over the same connection that brings the digital audio to
the loudspeaker. This will allow the integration of all
loudspeaker functions as part of the common virtual
sound system.
38.4.3 Processing System
Those portions of the audio processing that are not con-
tained either in the microphones or the loudspeakers will
be contained in the central processing system. This may
be either a single processor, or a networked array of pro-
cessors. In either case there will be a single user interface
for programming and controlling the entire system.
Control and monitoring of the virtual sound system
may occur from many locations concurrently. The
system will be controllable from PCs running either
dedicated control software, or even standard Web
browsers. For situations where control via a mouse is
not acceptable, touch screen controllers will be avail-
able. Where physical controls are desired, a variety of
standard, modular, control panel elements will be avail-
able. These will allow implementation of physical
controls as simple as a wall mounted volume control, or
as complex as a large mixing console.
Virtual sound processors have evolved substantially
since the first products of this type were introduced in
the early 90s. As the processing power available in
these products has grown so have the capabilities.
Sound systems exist in a real-world environment,
which also contains many other elements with which
the sound system operation must be integrated. The
most advanced of today’s virtual sound processors
contain powerful control logic subsystems to ease this
integration. High-speed control connections allow
exchange of data with external room and building
control systems.
QSC Audio recently introduced a new audio
processing product suite that has advanced the reli-
ability, sophistication, and capabilities of virtual audio
processing products. The QSC offering incorporates
many functions that previously were available only in
distinctly separate products. These include advanced
virtual devices such as FIR filters, feedback suppres-
sions, and ambient level sensing. It also greatly reduces
the amount of time needed to compile, as well as incor-
porates a very low, and fixed, latency between all inputs
and outputs. The QSC product allows the designer to
easily create a fully redundant system, answering much
of the concern that was initially generated by the use of
digital systems for all of a facility’s audio signal
processing and control.
One very significant advantage of the most advanced
virtual sound processing systems is the ease with which
it is possible to make the various processing subsections
interact with each other. For example, an automatic
microphone mixer can be thought of as multiple-level
meters and gain blocks, where the signal level at the
various inputs is used to adjust the instantaneous gain of
the various gain block. Such automatic microphone
mixers exist in analog, digital, and virtual form.
However, that sort of interaction can be expanded
greatly to the system level in a virtual sound processor.
For example, each microphone input processing chain
might contain an AGC. The maximum possible gain an
individual AGC can insert while still keeping the entire
sound system stable will depend in part on the amount
of gain or loss the AGCs for every other microphone are
applying. In a virtual system it is possible to let each
AGC know what the other AGCs are doing, and based
on that information modify its behavior.
There are devices on the market that dynamically
insert notch filters to keep a sound system from going
into feedback. They do this by monitoring the onset of
feedback and very quickly applying the corrective
filters. This means the system must slightly start to ring
before correction can be applied. A virtual sound
system, by contrast, can monitor all the factors that
impact system stability and insert corrective notch
filters selectively in only the signal path required, and
do so before the system starts ringing.
A virtual sound system can be programmed to know
which are the most critical microphones and loud-
speaker zones, and if trade-offs must be made to get
optimum performance, can optimize the most impor-
tant inputs and outputs. For example, if there is a person
who must be heard, and that person is speaking in a
very soft tone of voice and as a result the gain can’t be
gotten high enough, the virtual sound system can bring