AI
Most background-noise problems in a home recording are a steady hum, hiss, or fan whir sitting underneath your voice — a constant sound your ear tunes out but a microphone captures at full volume. The good news is that removing that specific kind of noise doesn't require paid software: Audacity, a free and open-source audio editor, has a Noise Reduction effect built for exactly this, and it runs entirely on your own computer.
How Audacity's noise reduction actually works
1. Find a noise-only stretch. Somewhere in your recording there's usually a moment of silence — before you start talking, or a pause — that contains only the background hum with no voice. Select at least half a second of it.
2. Get the noise profile. With that stretch selected, go to Effect > Noise Reduction and click "Get Noise Profile." Audacity analyzes the frequency pattern of that noise and stores it — this step doesn't change your audio yet.
3. Select the full track and apply. Select the whole recording, open Effect > Noise Reduction again, and click OK. Three sliders control the result: Noise Reduction (how many dB to attenuate), Sensitivity, and Frequency Smoothing — pushing Noise Reduction too high introduces a warbly "underwater" artifact, so start around 6-12 dB and increase only if needed.
| Noise Type | Works Well With Noise Reduction? | Why |
|---|---|---|
| Fan/AC hum, room hiss, electrical buzz | Yes | Constant frequency pattern the profile step can learn |
| Fluorescent light buzz, tape hiss | Yes | Also steady/stationary noise |
| Traffic, crowd chatter, a barking dog | No | Irregular, changing frequency content — no stable profile to subtract |
For that second category — irregular, non-stationary noise — there isn't a reliable free desktop fix; that's the gap that paid, AI-based real-time tools like Krisp are built for, since they use a trained model rather than a static frequency profile. But for the everyday case of a hummy laptop mic or a whirring fan behind your voice notes, Audacity's free Noise Reduction effect handles it well, and it costs nothing and never uploads your audio anywhere.
Practical Challenge
Record 10 seconds of yourself talking with a fan or AC running in the background, including a couple of seconds of silence at the start. Open the file in Audacity, get a noise profile from the silent stretch, and apply Noise Reduction at 12 dB — then compare it to the original.
Concept Check
Sources & Further Reading
- Audacity — Noise Reduction — official feature page confirming the tool is free/open-source and explaining the noise-profile mechanism and the noise types it targets.
- Audacity Support — Noise Reduction & Removal — official documentation on the Get Noise Profile / apply workflow and slider settings.