Extron Electronics MPX Plus 866 A Rev. B - Manual (Page 145)

5-39 MPX Plus 866 A Media Presentation Matrix Switcher • Switcher Software
PRELIMINAR
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Adjusting the post-matrix trim
Adjusting the post-matrix trim is a bit of a balancing act. This section provides
guidelines, but it may take a bit of going back and forth to set levels just right.
For example, the output level can be controlled and kept below clipping using a
compressor or limiter in the output dynamics block. However, adjusting the post-
matrix trim affects how the compressor or limiter works.
1 . Open the output volume dialog box and the post-matrix trim dialog box.
2 . Set output volume to 100% (if the audio is too loud or distracting, mute the
output).
3 . With program material or pink noise present at the input, adjust the post-
matrix trim until the output volume dialog box’s meter level is below clipping
(or ideally, matches the level at the input gain meter). This maintains the
audio at an optimal level in the output signal chain, and prevents clipping at
the output.
Setting the volume control for the amplifier stage
The switcher’s maximum output is +22 dBu. Assume that you have a power
amp with a maximum input level of +4 dBu when the input attenuator is fully
open. If you want to control volume levels using the switcher’s non-DSP
output volume controls and at the same time ensure that clipping does not
occur at the amplifier, you need to turn down the power amp’s input attenuator
the equivalent of 18 dB (18 + 4 = 22 dB), which puts the amp’s input level at
-14 dB (+4 minus 18 = -14). If you find that the amp setting (when the DSP
Configurator’s output volume controls are at 100%) is too loud for the room, you
can turn it down further. If the amp is not loud enough for the room, you will need
a more powerful amplifier.
On the other hand, if you wish to control volume levels using the power amplifier’s
input attenuation control, (using the same power amp max input level) you can set
the DSP Configurator’s output volume control to -18 dB. This is another way that
clip points of the two devices will be matched, ensuring that clipping will not occur.
However, Extron recommends using the matrix switcher’s output volume control
for controlling output volume. If you are using loudness processing on the unit, it
works only in conjunction with the output volume control.
Calibrating loudness
The basic gain structure is now set up. From this point, loudness can be calibrated
using an SPL meter, a critical ear, or a combination of the two.
Setting loudness using a meter
To calibrate loudness, use a sound pressure level meter set to “C” weighting.
1 . Open the post-matrix loudness processor dialog box.
2 . Bypass the loudness processor.
3 . Place the meter in an average listening location.
4 . Start your program material playback or generate pink noise.
5 . Measure the SPL in the room.