Removing White Noise from an Audio Track

Audacity is a free audio editor. Among the various features, we are going to focus on noise removal.
This tool will be helpful if you are recording dialog and want to remove white noise. You need to be sure to record a few seconds of ambient noise so that you have a good sample. This works best if you are removing a constant hum.

Open your audio file, then using your mouse to click and drag, select a portion of white noise, that is devoid of any dialog or sound you want to keep.

The white noise sample is selected.