Owner`s manual
35
Operating Manual - nX, nXe, and nXp Power Ampliers
Background Information
The feedback suppressor uses both notch lters and parametric lters to automatically and quickly suppress multiple
feedback tones and also produce a smooth equalized response which sounds pleasing for music and speech program. Before
using the FBS (Feedback Suppressor), it is helpful to understand the following basic concepts in order to effectively suppress
feedback and achieve good sounding audio program.
Each of the 12 FBS lters available on each FBS input channel can be selected between three different modes:
Restricted - The lter's attenuation level can only be made deeper, or lter bandwidth made broader by the FBS.
Floating lter - The lter's parameters are dynamic in that the FBS will slowly remove the lter if no
longer needed and redeploy at a different frequency as needed. Only oating lters are affected by the Float
Time parameter which is the time after which the FBS will slowly remove the lter.
Manual lter - The lter is not automatically controlled by the FBS, but can only be controlled by the user.
The FBS will automatically use available restricted lters rst. If there are no more restricted lters available, the FBS
will automatically use oating lters. The FBS will not automatically change manual lters.
The Sensitivity Control simply adjusts how sensitive the FBS algorithm is to detecting feedback and inserting lters.
For example, a setting of Very Sensitive means the algorithm will aggressively look for anything that could be feedback and
hence it may often insert lters on musical tones. A setting of Very Insensitive means that the FBS would only insert a lter
in the presence of a prolonged feedback tone with very little background noise. The optimal setting of the Sensitivity control
depends on both the spectral content of the audio program (how much the musical instruments sound like feedback), and also
on the amount of background music and noise which tends to mask feedback from the detector. It is best to start with an Average
Sensitivity setting and experiment.
A Locked lter means that the lter is prevented from being changed in any way, either automatically by the FBS or
manually by the user. To change or reset a lter, it must rst be unlocked.
FIR Filter (Outputs only)
The FIR (Finite Impulse Response) lter is typically used when a speaker manufacturer develops a proprietary
FIR coefcient le that corresponds directly to their own loudspeaker or speaker cabinet, addressing frequency and phase issues
based on their own measurements and formulations. Plugging in a FIR lter block on a DSP output and then clicking on it will
prompt the user for a *.r or *.csv text le, which is then loaded and applied to the output DSP. The two le types will have
identical coefcient code, however the *.r le may add comments (designated by a semi-colon) or a key=value pair denition
such as sample rate. Either le type will work with Protea
ne
Software.
Simple *.r le example:
; comments section
sampleRate = 48000
+0.0000042920
+0.0000030236
-0.0000040482
Simple *.csv le example:
+0.0000042920
+0.0000030236
-0.0000040482
Note that Protea software does not offer the ability to view or edit the EQ curve produced by a FIR lter. Also, FIR lters
are very DSP intensive, so if a FIR lter is used on an output channel, that same numbered input channel's Feedback Suppressor
will not be available in order to allocate enough DSP power to the FIR lter.