Remove hum and hiss from audio
Hum is usually tonal (frequency-specific). Hiss is usually broadband (noise-floor). Treat them differently for clean output.
Hum vs hiss (fast identification)
| Signal | What you hear | What you see (typical) | Primary fix |
|---|---|---|---|
| Hum | Low pitched tone, constant | Discrete peaks at 50/60 Hz + harmonics | Notch filter (narrow), then light denoise |
| Hiss | “Shhh”, steady noise floor | Broad energy across high frequencies | Denoise / spectral reduction |
If you have both: remove hum first. Otherwise denoise can turn hum into a wobbling artifact.
Common causes (so you can prevent it next time)
Hum (50/60 Hz)
- ground loops (multiple powered devices connected)
- unbalanced cables picking up interference
- power supplies near audio cables
- guitar pickups / noisy adapters
Hiss
- preamp gain too high (low input level, boosted later)
- cheap/noisy mic preamps or interfaces
- wireless links and RF noise
- distance-to-mic too large (low SNR)
80/20 order of operations
- Check clipping: if it’s distorted, denoise won’t restore missing peaks.
- Remove hum: notch the fundamental + harmonics carefully.
- Denoise hiss: conservative reduction; avoid re-voicing the speaker.
- Level: apply compression/limiting after noise is reduced.
- Verify: listen for speech thinning, metallic hiss, and pumping.
How to remove hum (without killing the voice)
- Target the exact frequency: 50 Hz in many regions, 60 Hz in others—confirm by listening/analysis.
- Use narrow notches: reduce the tonal peaks while leaving neighboring speech energy.
- Handle harmonics: hum often includes 100/120 Hz, 150/180 Hz, etc.
- Avoid wide cuts: the voice fundamental often sits around ~85–255 Hz; wide filtering can thin speech.
If the hum changes pitch or warbles, treat it as a more complex problem; notches alone may leave residue.
How to remove hiss (without “watery” artifacts)
- Prefer moderate reduction: aim for intelligibility and comfort, not absolute silence.
- Protect sibilance: “s/sh/f” sounds can be mistaken for hiss.
- Multiple light passes: two gentle denoise passes often sound cleaner than one heavy pass.
- Keep room tone: a small stable background is more natural than dead silence.
Artifact troubleshooting
Metallic voice
- Reduce denoise strength.
- Check that sibilants aren’t being removed as noise.
Voice sounds thin after hum removal
- Narrow the notch bandwidth.
- Don’t notch frequencies that overlap strongly with voice fundamentals.
Pumping between words
- Use less aggressive thresholds; avoid hard gating behavior.
- Allow a small amount of stable room tone.
FAQ
Should I EQ before denoise?
Usually hum removal first is fine. Avoid aggressive tonal shaping before denoise; it can confuse the noise estimator.
Can denoise remove hum?
Sometimes, but tonal hum is best removed with targeted filtering. Denoise alone can leave artifacts or residual tones.