DMPA12 Digital Power Amplifier
LECTROSONICS, INC.
2
Limiter Tab
The limiter implementation is based on an RMS level
detector controlled by a single time constant param-
eter. This is an adaptive design which responds to
varying rates of change in the signal level by dynami-
cally adjusting the attack and release times for best
performance.
Note to those accustomed to specifying
separate attack and release time constants:
Select a time constant parameter that is about
one-half the release time constant you would
normally choose. Don’t worry about the attack
time constant, the true RMS detector based
compressor or limiter will always put into effect
an optimal value. The greater the rate of increase
in signal level, the smaller (more aggressive)
the attack time constant will be. The default time
constant value is 100 ms, corresponding to a
release time constant of about 200 ms.
This tab contains a notebook of output limiter settings,
with a separate page for each output channel. If con-
nected to a DMPA12, changes made in this tab take
effect immediately. As always, the changes are not
permanent unless the DMPA12 settings are stored to a
preset in nonvolatile memory.
The tabs along the bottom of the output channels
notebook are used to select the settings for a particular
output channel. On each page the following controls
and indicators are always visible:
• Limiter setup
• Amplitude response graph
• Gain reduction meter
• Compressor status indicators
• Limiter status indicators
Limiter setup
Limiter parameters are set by the following numerical
controls:
•
Threshold
The limiter input level threshold is displayed here
and can be adjusted from -80dBu to +20dBu.
•
Time Constant
The limiter time constant is displayed here and can
be adjusted from 0.1 to 500.0 ms.
For any of these controls, there are two ways to change
the value:
Click on the buttons next to the control to run the value
up or down
Type a value directly into the control and press ENTER
Limiter setup parameters for one output channel can be
copied and pasted into another output channel. There
are two ways to do this:
Right click within the Limiter setup group for the source
output channel and choose Copy Limiter from the
popup menu. Then select the page for the destination
output channel, right click on Limiter setup group, and
choose Paste Limiter from the popup menu.
With the source output limiter page selected, choose
Edit->Copy Limiter from the Menu Bar. Then select the
page for the destination output channel and choose
Edit->Paste Limiter from the Menu Bar. If you wish to
paste the copied limiter settings to ALL output chan-
nels, then choose Edit->Paste Limiter to ALL from the
Menu Bar instead.
Compressor activity
Limiter activity
Threshold value
Time Constant
Reference amplitude
response (dashed grey)
Compressor amplitude
response (orange line)
Limiter threshold
(dashed red)
Total amplitude
response (solid blue)
