I have a cheap Behringer noise suppressor (an old model now out of production). Its adaptive notch filters can be "freezed" once they are set for the particular application, so they don't move around during the performance. It saved my day several times with an amped acoustic guitar that simply wouldn't behave nicely. Yes, of course it changes the sound, but the extra headroom can be HUGE: not just a couple of dBs, but the difference between having to keep the guitar almost completely unamplified and hearing it clearly in the mix.