Setting Mic/Line Input And Mix Levels; Adjusting Trim; Setting Volume Control For The Amplifier Stage - Extron electronics DMP 128 User Manual

setting Mic/Line input and Mix Levels

In this example, the mic/line input 1 signal is sent to output 1. To set the mic/line input and
mix levels:
1. Connect a microphone to Input #1.
2. Double-click the mix-point (see figure 63, c on page 101) for mic/line input 1 to
output 1 to open the dialog box for that mix-point, and unmute the mix-point to place
that signal into the mix.
The default level for the mix-point is 0 dB, or unity gain.
3. Open the input 1 Gain (see figure 63, a ) dialog box and set gain to 0 dB (turn on
phantom power if the mic requires it), then unmute the channel.
4. While testing the mic, raise the fader level until the mic is clearly audible. The amount
of gain and the meter level reading vary at this point, but as a general guideline the
input gain level is adjusted to 40 to 50 dB, with the meter averaging somewhere
around – 20 dBFS.
Although audio is optimized here, voice levels at mic inputs can vary greatly and further
adjustment can be necessary. When the meters average around – 20 dBFS, enough
headroom is available to accommodate sudden changes to voice levels.

adjusting trim

This is where setting gain structure becomes a balancing act. The following sections
provide guidelines, but it may take a bit of going back and forth to correctly set levels for
the installation. For example, 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 will affect how the compressor or limiter works.
1. Apply program material (or pink noise) at the input being adjusted.
2. Open the output Volume ( e ) and post-matrix Trim ( d ) dialog boxes (see figure 63).
3. Set output Volume to 100% (mute if necessary).
4. Adjust the post-matrix trim until the meter level in the output volume dialog 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 Volume control for the amplifier stage

The maximum output of the DMP 128 is +21 dBu. As an example, assume the maximum
input level of a power amp is +4 dBu with its input attenuator fully open. If using the
output Volume control (see figure 63, e ) of the DMP 128 to control volume levels, to
ensure clipping does not occur at the amplifier, turn down the input attenuator of the
power amp the equivalent of 17 dB (21 – 4 = 17). That puts the amplifier input level at
– 13 dB (+4 – 17 = – 13). If the amplifier setting (when the output volume controls of the
DMP 128 are at maximum) is too loud for the room, it may need further reduction. If it is
not loud enough for the room, a more powerful amplifier may be required.
Extron recommends using the output volume or post-mixer trim control on the DMP 128
for controlling output volume. If using loudness processing on the unit, it works in
conjunction with these controls.
Using the power amplifier input attenuation to control volume (using the same power amp
maximum input level) set the output volume or post-mixer trim control of the DMP 128 to
– 17 dB. This is another way that clip points of the two devices are matched. Verify the
amplifier is not clipping by observing the amplifier clip indicator.
notE: Using the amplifier input attenuation to control volume compromises the
signal-to-noise ratio of the DMP 128, and is not recommended.
DMP 128 • Software Control 104