Advanced Feedback Suppression (Afs) - dbx DriveRack PA2 Owner's Manual

®

Advanced Feedback Suppression (AFS)

Feedback is caused when an in-phase audio loop is created between an input transducer (such as a guitar pickup or
microphone) and an output transducer (a loudspeaker). The DriveRack PA2 includes the exclusive AFS
Suppression ) algorithm to help combat this dreadful phenomenon.
™
The AFS algorithm in the PA2 is a little different than the AFS algorithm used in any previous dbx products. That's because
the dbx engineers revisited the already-stellar AFS algorithm to see if they could improve it. And guess what? They did! The
updated AFS algorithm in the PA2 can now detect and eliminate feedback faster than ever before and with even higher
precision. The updated AFS algorithm offers the following enhancements:
• It is faster at eliminating the offending feedback frequency.
• It can better determine what is actually feedback, making it far less likely to set false triggers on feedback-like audio
sources, such as a flute.
• It can better determine how much attenuation is required to notch out the feedback, resulting in notch filters which aren't as
deep and even less audible.
• It prevents the filters from being too narrow to tackle feedback at lower frequencies.
• It has better frequency resolution, which provides pinpoint accuracy and uses the narrowest filters possible.
• When lifting Live filters, the filters are lifted more gradually to better determine if it is safe to lift the filter, preventing blaring
feedback from suddenly returning.
AFS uses precision frequency detection and state-of-the-art processing to determine the exact range of feedback frequencies
to remove (instead of indiscriminately removing large sections of audio). In the past, graphic equalizers were used to eliminate
feedback from a system. This was an acceptable method for eliminating feedback, but when this method is put up against
precision notch filters, such as those found in AFS, it becomes very evident that using graphic equalizers for this task severely
affects the tone of the system. With AFS, the precision filters remove only a fraction of the frequency spectrum, eliminating
the feedback with far less audible artifacts. The below diagram shows a comparison of filter widths between the AFS filters,
conventional 1/3 octave EQ filters, and notch filters used in competitor's feedback elimination processors.
Filter Precision Comparison Chart
(Advanced Feedback
™
31