dbx Pro User Manual for Efficient Feedback Control with dbx AFS 224

Operation User Setup

AFS 224

C-1 Ringing out a system

Fixed mode filters are set before a performance in a process called "ringing out a system". This is done after all other system EQ'ing has been done. First, bring down the main mix, turn off all music sources and open all the mics. Place the AFS 224 into fixed mode by pressing the <MODE> button for the channel. A <MODE> button lighting green indicates Fixed mode for that channel. Select the channel’s filter type by pressing the channel’s <TYPE> button. See Using Types in Fixed mode below. Slowly turn up the main mix, raising the gain of the system, until feedback occurs. The AFS 224 will detect and remove feedback by placing notch filters at the feedback frequency. Continue to slowly raise the gain until all feedback has been eliminated or all fixed filters have been used, this will be indicated by the flashing <MODE> button.

C-2 Using Types in Fixed mode

The AFS 224 offers several feedback suppression types. These are Speech, Music Low, Music Medium and Music High. The selected type controls the width of the notch filter used to remove the feedback. Music High uses very narrow notch filters minimizing the effect on the music. The Speech type uses much wider notch filters allowing the AFS 224 to work faster. See Type in Front Panel section for descriptions and indicators.

AFS 224 Filter Q's

	+3							+3
	+2							+2
			Music High - 1/80th Octave
	+1							+1
	-0							-0
	-1							-1
	-2						Music Med - 1/20th Octave	-2
d									d
B	-3							-3	B
u	-4						Music Low - 1/10th Octave	-4	u
	-5						Speech - 1/5th Octave	-5
	-6							-6
	-7							-7
	-8							-8
	-9							-9
	700	750	820 850	900	.95k	1k	1.2k
						Hz

During the filter setting process the filter type can be changed by pressing the channels <TYPE> button. This will change the filter type for the next filter and will not change exist- ing filters. When all fixed filters have been used new feedback occurrences will not be removed. Pressing the <MODE> button will place the AFS 224 into Live mode (indicated by the <MODE> button lit Red) and feedback will continue to be removed. If more fixed filters are needed, reallocate more filters by following the steps in Setup Mode or clear the filters (See section E-Clearing Filters) by pressing and holding the <BYPASS> button until all the Filter LED's blink and repeat the procedure above with a wider filter type.

D - Using Live Mode

Live Mode allows feedback filters to be set and removed based on changes in the environment and is designed to be used during a performance. The AFS 224 can be put into Live Mode by pressing the <MODE> button until it lights red. Once in Live Mode, if feedback occurs a fil- ter will be set at the feedback frequency. If there are additional occurrences of feedback, addi- tional notch filters will be set until all the Live Filters are used. If new frequencies begin to fee back and no more Live Filters are available, the AFS algorithm will take the first Live Filter set, and move it to the new feedback frequency. The AFS 224 will continue to “round robin” through the Live Filters as new feedback is detected.

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5 3AFS 224 User Manual