Squuueeeeeeaaaaccchh! You know it in an instant: that piercing, ear-melting shriek blaring out of your loudspeakers. It&#;s feedback, and it&#;s a showstopper&#;in more ways than one.
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Feedback, the high-pitched wail generated when a signal loop builds between a sound system&#;s audio input (here, a microphone) and amplified output (speaker), can happen anytime, anywhere. Feedback dangers lurk all around you: Common offenders include singers cupping mics, presenters on wireless mics wandering into danger zones onstage, incorrect placement of floor monitors, even fluctuations in air temperature and humidity. And, feedback isn&#;t just an annoying noise; it can cause irreparable damage your loudspeakers&#;and your ears.
There are many ways to reduce the potential for feedback, including introducing noise gates, EQing problem frequencies, lowering gain, switching to a more directional microphone, or simply moving your mic closer to the sound source or out of a loudspeaker&#;s line of fire. To maximize volume before feedback, live sound engineers &#;ring out&#; P.A. systems by methodically bringing up system levels until feedback occurs, EQing out problem frequencies and repeating the process until the system is optimized.
Feedback can occur at any frequency, and is often caused by a confluence of factors. If you&#;re not a professional audio engineer, it&#;s easy to find yourself chasing a solution through endless trial and error&#;or worse yet, leaving your show up to chance. Luckily, there&#;s a safety net. Automatic Feedback Suppression, and for more control, Advanced Feedback Suppression&#; (AFS), a dbx patented algorithm is available in several dbx products, which uses sophisticated filters and algorithms to take the guesswork out of feedback management.
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Automatic Feedback Suppression works like this: The algorithm monitors incoming audio for signs of feedback; when it detects feedback behavior, it places a narrow notch filter at each frequency that feeds back, reducing the gain of that frequency. Ultra-precise, 1/80-octave filters carve out offending frequencies with pinpoint precision, preserving as much of the surrounding frequency spectrum as possible, which in turn preserves overall sound quality. This process takes just milliseconds, and is complete before the human ear can detect anything amiss.
Automatic Feedback Suppression is easy to use: Just set your desired level of suppression and it works automatically. Choose your level of control, from the totally preset press of a button Automatic Feedback Suppression feature in products like JBL IRX Series loudspeakers to the advanced (AFS®) functions in processors such as the dbx AFS2 Advanced Feedback Suppression processor and DriveRack PA2, which let you opt for a setup wizard or dig into finer parameter control, whether you&#;re ringing out your system or protecting your system during your show.
Automatic Feedback Suppression technology makes managing feedback fast and easy. With a little practice and thorough sound checks, you&#;ll be a pro at stopping feedback in its tracks, so you can keep the focus where it belongs: on your performance.
As a live sound engineer these types of devices can be problematic:
The removal of frequencies usually causes things to sound worse, and at best it usually allows for additional 6dB or so of gain before feedback starts to occur at many-many frequencies. It is at this point that "diminishing returns" have been hit, and further EQ here is in effect turning down the gain.
Every live system has a fixed gain before feedback, that is independent of the level of the source. Perhaps a system (microphone -> Console -> Loudspeaker) is capable of adding +20dB to the volume of the source. This capability is the same whether the source is whispering or shouting; the difference is that +20dB may not be loud enough to properly reinforce the person whispering.
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If I am doing my job well as an audio engineer in the live domain, feedback will never be heard. I rarely use any sort of EQ notch for this, that is a last resort, as EQ is not the best tool for this job.
Avoiding feedback often comes to down loudspeaker deployment (and understanding how that type of loudspeaker interacts with the space around it), overall gain, and microphone selection. Specifically the pickup pattern is quite important. Especially if wedges are being run, vs IEM's, understanding the pickup pattern of mics and using that to guide wedge placement is critical.
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In my opinion the product above has no place in anything other than live-sound, and its merits there are dubious at best.
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