How does the DFR11EQ determine feedback from music tones?
If feedback is being used in a "musical manner", like a rock quitarist, the DFR11EQ cannot tell the difference. It will attack the feedback. Or a note held on a pipe organ might also be "pure" enough to fool the DFR11EQ.
Most musical notes vary enough in pitch (vibrato) and level that the DFR11EQ can distinguish these notes from feedback, as feedback does not vary in pitch and normally rises in level.
In a musical application, it is best to "ring out" the PA system ahead of time and then lock down the DFR11EQ so that it does not mistake a pure musical tone for feedback.