I would never call myself an expert, but I do have experience with
feed back. I definately think the first thing is find out what is causing it.
I know you know the obvious stuff like making sure your speakers and
monitor are placed correctly. Usually with my system I have to adjust the monitor
settings, more on the main control than individual settings. If that isn't it I double check my eq on the mains and monitor. I've never gotten feedback from fx. I preset my gain and my eq to each venue to make sure it won't cause feedback ahead of time, so I'd go to that last.
The question about frequency - I can usually tell if it is low or high by the sound. If that is what you are asking.
Are you asking for yourself or in general. I know you know this stuff.
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