DTP CrossPoint 4K Series Matrix Switchers • Matrix Software 148
Optimizing the Audio
Program material that you are familiar with is preferable for the following procedures,
otherwise, pink noise can be used.
TIP: The Extron VTG 300 or VTG 400 is recommended to provide the pink noise.
Input Clipping and Clipping Meters
Audio clipping is a form of distortion that occurs when the signal peaks (or excursions)
exceed the limits of the circuit, cutting off the excursions of a signal. This condition gives
audibly undesirable results. While it is difficult to clip the audio signal within the DSP audio
signal chain, it is extremely important that the audio signal is not clipped before the input to
the switcher. Once audio is clipped at the input, there is no remedy further down the signal
chain. However, if audio clipping occurs at the output of the DSP that is not a result of
clipping at the input, this can be addressed in the DSP audio signal chain.
Meters are available in the gain controls ( ) and in the dynamic processor blocks ( ) when
the program is in Live mode and an audio signal is applied to the DSP. The meters in the
DSP Configurator program indicate clipping at a user-definable level, with the default setting
at -1 dB. At the -1 dB setting, the meter indicates clipping when it reaches -1 dBFS, or 1 dB
below actual clipping. Setting the clipping meter below actual clipping provides a bit of a
“safety net,” letting you know to pull back on input gain before clipping actually occurs. You
can increase or decrease this safety net by clicking Tools > Options > Defaults tab >
Meter Clipping tab, and setting the Clip
Threshold to a number between 0 (dB) and
-20. When the clip threshold is set to 0, clipping
is indicated only when actual clipping occurs.
Meters within the DSP Configurator program are peak-type meters, referenced to “full
scale,” or 0 dBFS. For the DTP CrossPoint 4K Series, 0 dBFS corresponds to 22 dBu,
which is the maximum output level of the switcher.
Setting the Input and Output Gain Structure
Before calibrating loudness, set up the system gain structure.
1. Set the signal generator to output -10 dBFS or use recorded program material at
-20 dBFS.
2. Set the input gain in the DSP Configurator so that the input meter reads -20 dBFS.
NOTE: In step 3, if using a recorded source and the player has an output level
setting control, ensure that the output of the player is set to its maximum, or 0 dB
of attenuation.
3. For program material, set the input level to approximately -15 dBFS, with peaks
at no more than -5 dBFS to -3 dBFS. This setting provides enough headroom to
accommodate transients or unanticipated loud events in the program material in order
to avoid possible clipping.
4. Tie the audio from the source to the speakers that will carry program material in the
room to be calibrated.
5. With the output channel volume set to -20 dB, listen to the audio output while you
set the external amplifier so that the source material plays at a volume level that is
reasonably loud but tolerable. Verify that the amplifier is not clipping by observing the
amplifier clip indicator.
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