Cleaning up a voice recording? Keep a few seconds of the room.

Before recording a short explanation for a customer, leave a few seconds with nobody speaking. Keep the microphone in place. That bit of room noise can be useful later. Audacity's existing Noise Reduction effect uses a sample of the unwanted sound. Its support guide says to select a few seconds containing only background noise, open Noise Reduction and choose Get noise profile. Then select the audio you want to clean and open the effect again. Preview before applying it. For a steady fan hiss, I'd try this on a copy before paying for an AI audio cleaner or recording the whole explanation again. It isn't the right fix for every sound: Audacity's manual says irregular traffic or audience noise is unsuitable for this effect. The handy control is Residue: it lets you hear what would be removed. If you hear recognizable bits of your voice there, the manual says Noise Reduction or Sensitivity may be too high. Back off, and switch back to Reduce before applying. A little hiss is preferable to losing words. This is a suggestion from the documentation, not an audio test I've run. You don't need a perfectly silent recording to explain how something works; you need the listener to hear you comfortably.