Remove mains hum

What it does

Removes the low, steady electrical buzz that gets into recordings from power supplies, ground loops and badly shielded cables. It checks your file for both 50 Hz and 60 Hz hum, removes the one it finds along with its first four harmonics, and tells you what it found.

How to remove hum

1. Open the recording. Remove hum is ticked.
2. Listen, and read What was done: it reports the hum frequency and how far it stood above the background.
3. If hiss remains too, tick Reduce noise.
4. Export the result.

Why recordings hum

Mains electricity alternates at 50 Hz across most of the world and 60 Hz in the Americas and parts of Asia. That frequency leaks into audio gear, along with harmonics at 100, 150 and 200 Hz or their 60 Hz equivalents.

The fix is a set of very narrow notch filters at exactly those frequencies, so almost nothing else is touched. A simple high-pass filter would remove the hum by removing your bass along with it.