Extron electronics MediaPort 300 User Manual page 75

Adjusting the Output Levels —
Since the USB output and the analog Line outputs contain mixes of different audio signals,
it is important to test the system and monitor these outputs to ensure that the signal level
approaches 0 dBFS with enough headroom to avoid clipping. If the meters show clipping,
the fader control on the output can be lowered to bring the signal down below 0 dBFS. If
clipping occurs at the input and lowering the output fader control does not eliminate the
clipping, the input gain must be lowered.
If the output meter shows clipping and there is no clipping occurring at the input, then
lowering the output fader control eliminates the clipping in most cases. Within the
MediaPort 300 digital signal path, there is a certain amount of headroom, such that a signal
or mix of signals that is too hot at the output can be lowered at the output fader control to
eliminate clipping.
If lowering the output USB, Line 1, or Line 2 fader control prevents clipping at the output
meter, but clipping is still audible (and there is no clipping present at the input meters), then
levels must be lowered in the Mix page to eliminate clipping. The Room Volume fader in the
Near End panel (and the Mic and Program controls in the Mix to Far End section) are all
master controls that include soft limit controls. Setting the soft limit so that the fader cannot
go above a level that causes clipping is a method of controlling clipping from the Mix page
Mix Page DSP
(see on page 45). Otherwise, it is necessary to lower faders in either the
Program Mix section, the USB Communications fader, or both. Check the output meter
often to verify that clipping does not appear on the meter.
Connecting to an Amplifier —
When the line output is connected to a sound reinforcement system, the sound system
amplifier must be set to accommodate the output level of the MediaPort 300. If adjusting
the amplifier input sensitivity instead of the MediaPort line output level, the Line output
attenuation controls set to 0 dB gives the best signal-to-noise results.
Sound Reinforcement System —
A typical sound reinforcement system includes a power amplifier, such as the Extron
XPA 102 Plus, and speakers, such as the Extron SM 26. In most cases, the input
sensitivity of an amplifier has a maximum of +4 dBu. The max output of the MediaPort 300
is +21 dBu, so attenuation of the amplifier input sensitivity is recommended. An input
sensitivity of -12 to -17 dB on the amplifier should work well, but this may require testing the
system and fine-tuning the settings. The target SPL level for the application must also be
taken into consideration.
The gain structure article referenced earlier in this section suggests an amplifier input setting
of 12 o'clock, which usually falls in the aforementioned range. The 12 o'clock setting is
convenient and easily repeatable, making it a recommended best practice.
MediaPort 300 HDMI and Audio to USB Scaling Bridge • Standalone Application Setup 67