Virtual Systems 1449Let’s take our previous example of a loudspeaker
processor with three inputs, each optimized for a
different type of program, and three-way outputs, and
design a virtual sound processor for this task using QSC.
Other virtual sound processors could also be used for the
same purpose although some details would be different.
The first step is to place the virtual devices for the
audio inputs and outputs. Since we wish analog inputs
and outputs, we will select analog I/O cards for inputs
and outputs 1 through 4 from the Device menu,
Fig. 38-10.
Input 1 will be our speech input. We will use a high
pass filter, a 1 band parametric equalizer, a high-
frequency shelving equalizer, a compressor, and a three
input mixer. Input 1 will wire to the input of the high
pass filter. The output of the high pass filter feeds the
parametric equalizer, which feeds both the main input of
the compressor, and the shelving equalizer. The output
of the compressor wires to the first input of the mixer.
The high pass filter will be adjusted to be a 125 Hz
Butterworth 24 dB/oct filter. This band limits the input
to the speech range, and prevents the entry of
low-frequency noise. The parametric equalizer will be
set for a bandwidth of two octaves, and 3 dB boost at
3 kHz. This provides a gentle emphasis of the speech
intelligibility range. The compressor is left at its default
settings of Soft Knee, 0 dB threshold, and a ratio of 2:1.
The high-frequency shelving equalizer will be set to a
frequency of 8 kHz, and 8 dB of boost. In combination
with the compressor, this serves as a de-esser. By
boosting the sibilance range at the input to the side
chain of the compressor, those frequencies will be
compressed more easily, and excessive hig-frequency
sibilance will be controlled, fIG. 38-11.
Input 2 will be for the background music. We will
use a high pass filter, two bands of parametric equaliza-
tion, and a compressor. The high pass filter will be set to
80 Hz with a Q of 2. This produces an underdamped
response with a bass boost just above the low-frequency
roll-off. One band of the parametric equalizer is set to
1.5 kHz with a bandwidth of two octaves, and a cut of
5 dB, while the other is set to 8 kHz with a bandwidth
of one octave, and a boost of 5 dB. The combination of
the high pass filter and the parametric equalizer
produces the desired background music response. The
compressor is set to Soft Knee, 10 dB threshold, and a
ratio of 4:1. This provides a more aggressive compres-
sion. The output of the compressor is wired to the
second mixer input.
Input 3 is for full range music. It has a high pass
filter, and a low-frequency shelving equalizer. The high
pass filter is set to 30 Hz at 12 dB/oct, and the
low-frequency EQ is set to +10 dB at 100 Hz. The
output of the EQ is wired to the third mixer input.
The output of the mixer will drive a 6 band para-
metric equalizer for overall system EQ. Next comes a
three-way 24 dB/oct crossover. The low-frequency
output of the crossover is wired to a high pass filter with
the Q adjusted so it optimally tunes and protects the
woofer. Next comes a three band parametric EQ, five
millisecond delay, and limiter. The side chain input of
the limiter is wired directly from the output of the EQ
bypassing the delay. This combination of a delay and
limiter wired so that the main input of the limiter sees aFigure 38-8. Inside a typical virtual device from QSC. This shows the sort of controls and indicators found inside the virtual
devices in Fig. 38-7.B. A sampling of the control and indicator styles available
in QSC. Controls inside Virtual Devices may be copied
into control panels, and arranged into user friendly
control screens.A. Inside a typical Virtual Device from QSC. This shows the sort of controls and indicators
found inside the Virtual Devices in Fig. 38-7.