Try as I may to elimate the chance for feedback during soundcheck, sometimes it happens during a show. That's life.

Sure, I have trained my ear throughout the years, but nothing allows me to do it quicker and more precisely than a good audio measurement app and a digital equalizer.

Nowadays I keep the Spectrogram running during shows, and if feedback happens, hopefully I can get a good reading. Then it's as easy as notching out the offending frequency via either a parametric or graphic EQ.

This is a screenshot of some feedback that just happened. You can see a vertical yellow line about two thirds of the way up in the middle of the screen. The screenshot doesn't show the frequency, but when I touch the screen within the app it will be displayed.

It's at precisely 4.35 kHz. Since this was from a vocal mic that is spread around multiple monitor mixes, I just went to that channel and took 4.35 kHz down by 12 dB. No more feedback.

It's surgical audio strike 

Cool.

I had my first taste of using audio equipment this weekend at a wedding. Wifes friend got married to a guy who is a hobbyist musician and his groomsmen were the guys he played with, so they set everything up. They told me if I heard any feedback to lower the mic input volume and adjust the main volume to make up for it. Only happened once and I guess it worked?

I imagine this app would have made it a bit easier to see, especially to my untrained ears. I have poor hearing anyway.

Sure, lowering the mic input volume will stop feedback (not sure about the latter instruction). That's more like carpet bombing the problem as opposed to my method of smart bombing it 

In other words, lowering the overall volume of the mic will bring the volume down across the entire frequency spectrum, when your problem is usually only one frequency (that of the feedback you're hearing). By the entire frequency spectrum, I mean every frequency you're capable of hearing, from the lowest bass to the highest treble.

If the feedback you hear is a screeching high-end whistle at say 4,000 Hz, why turn down everything seven octaves below that frequency? Why turn down everything two octaves above it? How about just turning down that particular frequency. This is what an equalizer allows you to do.

In the example in my original post, the singer likely never knows that I've done anything, because he doesn't perceive the absence of the one frequency I have cut. If I were to have reduced the overall volume of his mic, however, you can bet that he would let me know.

I understand that you were helping your wife's friend's new husband at a wedding, so not trying throw shade at all. This stuff takes practice. I just find it amazing that the tools for great sound reinforcement are cheaply available now on phones and tables, so just thought I'd share my methods for anyone interested in developing their sound dude chops 

Good lord, I wish there were more sound guys like you.

A real soundman would have just turned down the monitors and shrugged his shoulders at the band.

Thawntex is gonna get drummed out of the Soundman's Guild for stunts like this.

It will be the third strike against me for sure, the first two being that I don't have a ponytail and my name isn't Dave