Reduce steady background noise in Audacity without erasing speech

Audacity’s Noise Reduction can reduce steady sounds such as fan noise, hum and hiss. Use one selection to show Audacity the noise by itself, then another to check what it would remove from the recording.

Capture the noise

Suppose a recording has fan noise before the first word and beneath the speech. Select part of the opening that contains only the fan. Go to Effect > Noise Removal and Repair > Noise Reduction, then click Get Noise Profile. Audacity uses the selection to estimate the noise floor at different frequencies. Including a word would make it a poor sample of the fan alone.

Check what would be removed

Select the region you want to clean, including the speech, and open Noise Reduction again. Choose Residue and click Preview. You will hear the sound that Reduce would filter out.

Listen for recognizable syllables. If you hear them, lower Noise Reduction or Sensitivity and preview again. Lower Noise Reduction can leave more fan noise. Lower Sensitivity reduces the chance of losing speech but increases the chance of artifacts. When little wanted speech is audible in Residue, choose Reduce and click OK.

Audacity says the effect is unsuitable for isolated clicks or irregular noise such as traffic. Loud noise, or noise close to speech in level or frequency, may still cause distortion.

The steps come from the Audacity Noise Reduction manual. The fan recording is a hypothetical example.