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Operating Manual - nX, nXe, and nXp Power Amplifiers
Background Information
The feedback suppressor uses both notch filters and parametric filters 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 filters available on each FBS input channel can be selected between three different modes:
Restricted
- The filter's attenuation level can only be made deeper, or filter bandwidth made broader by the FBS.
Floating filter
- The filter's parameters are dynamic in that the FBS will slowly remove the filter if no
longer needed and redeploy at a different frequency as needed. Only floating filters are affected by the Float
Time parameter which is the time after which the FBS will slowly remove the filter.
Manual filter
- The filter is not automatically controlled by the FBS, but can only be controlled by the user.
The FBS will automatically use available restricted filters first. If there are no more restricted filters available, the FBS
will automatically use floating filters. The FBS will not automatically change manual filters.
The Sensitivity Control simply adjusts how sensitive the FBS algorithm is to detecting feedback and inserting filters.
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 filters on musical tones. A setting of Very Insensitive means that the FBS would only insert a filter
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 filter means that the filter is prevented from being changed in any way, either automatically by the FBS or
manually by the user. To change or reset a filter, it must first be unlocked.
