Fortunato asked how the anti-feedback device works.

Basically, you
Plug the mic into the device, and the device to the mic channel of the mixing board.

Set your mic equalization to your taste by using the board controls;
then: turn the volume UP until you get feedback, then lower the volume a bit till the feedback stops.
Here's the easy part: press the START button, and the unit searches for feedback frequencies--you can hear it working. Takes about 30 to 45 seconds.
It automatically notches out the feedback frequencies.

Presto! That's it.

Turn your PA volume up or down to suit your music. If it feeds back, reset the antifeedback unit , and do the process again.

Note that the AT 4033 requires phantom power. I generally power from the board, but the Roland device also will provide phantom power, via a selector switch.

The Roland will do more, but to this point in time, I haven't needed to explore that.

Rich McCarthy