can’t agree enough. Audio recordings are rarely improved with freeware editing and processing, even if you have pro software, you can only “polish a turd” so much. (industry term, calm down, admins.)
Proper microphone and preamp selection for your application will send you miles high than toiling for hours in Audacity or any DAW for that matter. Outside of a high-pass filter at about 250Hz, it’s best to keep your hands off.
A bad recording is like a bad photo, for example, if you shoot an image with extremely high ISO, there’s going to be hella “noise” (just like a phone mic or other not-purpose-built mics for full bandwidth recording) and there’s very little you can do (without professional software like PS or Topaz Labs stuff) that will “fix” the image without making it appear very unnatural, usually blurry or the like, the same applies for audio.
What you put in on the recording is the same thing you’re getting a playback, processing like EQ will only “mask” what you’re trying to eliminate (unless it’s a GML) it will generate a massive phase shift when frequencies are added or subtracted at their extremes, it’s the nature of how EQ works.
The best way to improve your recordings, is to make more recordings and make them better.
I think it’s very foolish to develop the habit of “fixing it in the mix”, it barely works, and it leads to a sub-par product and you’ll end up chasing your tail, especially if you’re trying eliminate noise, regardless of the source of it.
Sorry if I repeated myself or any of this seems unclear, I’m a bit under the weather today.
Happy to offer any advice or clarification for anything here anytime, I’ve been a professional audio engineer for longer than I’d like to admit :]