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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 (
c
) for mic/line Input 1 to Output 1 to open the dialog for
that mix-point and unmute the mix-point to place that signal into the mix.
The default level for the mix-point is 0dB, or unity gain.
3. Open the Input 1 gain (
a
) dialog and set gain to 0dB (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 will vary at this point, but as a general guideline
the input gain level should be at 40 to 50dB, with the meter averaging somewhere
around – 20dBFS.
Ideally, audio should be optimized here, but voice levels at mic inputs can vary greatly.
Having the meters average around – 20dBFS allows enough headroom to accommodate
sudden changes to voice levels. Further adjustment may be necessary.
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 to be adjusted.
2. Open the output volume (
e
) and post-matrix trim (
d
) dialog boxes.
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 while preventing
clipping at the output.
Setting Volume Control for the Amplifier Stage
The maximum output of the DMP128 is +21dBu. As an example, assume the
maximum input level of a power amp is +4dBu with its input attenuator fully open. If
using the output volume control (
e
) of the DMP128 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 17dB (21 – 4 = 17). That puts the amplifiers input level at –13dB
(+4 – 17=–13). If the amplifier setting (when the output volume controls of the DMP128
are at maximum) is too loud for the room, it may need to be reduced further. If it is not
loud enough for the room, a more powerful amplifier may be required.
It is recommended to use the output volume or post-mixer trim control on the DMP128
for controlling output volume. If using loudness processing on the unit, it will only work in
conjunction with these controls.
When 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 DMP128 to –17dB. This is another way that clip points of the two devices will be
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 DMP128, and is not recommended.
DMP128 • Software Control 105