How to Remove Hum and Buzz from Audio Recordings

That constant low-pitched buzz underneath a recording — even when nobody's speaking — is one of the most recognizable and fixable audio problems. Electrical hum contaminates thousands of recordings every day, from home studios to professional setups.

The good news: hum removal is one of the most reliably solvable audio problems. Because the interference follows a predictable pattern (a specific fundamental frequency and its mathematical harmonics), it can be removed surgically without affecting the wanted audio signal.

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What Causes Electrical Hum?

Electrical hum in audio recordings comes from electromagnetic interference from the power grid. Power systems around the world operate at either:

• 60Hz — North America, most of Central and South America, parts of Asia
• 50Hz — Europe, UK, Africa, Australia, most of Asia, Russia

The interference isn't just at the fundamental frequency — it appears at mathematical multiples called harmonics:

50Hz system: 50Hz, 100Hz, 150Hz, 200Hz, 250Hz, 300Hz...
60Hz system: 60Hz, 120Hz, 180Hz, 240Hz, 300Hz, 360Hz...

The fundamental is usually the loudest; each harmonic is quieter than the previous. But in recordings with significant interference, harmonics can extend to 500Hz or higher and still be audible.

Common Causes of Hum in Recordings

Ground loops: The most common cause. When two pieces of audio equipment are connected (microphone to interface, interface to mixer, etc.) and are also both connected to different electrical outlets or power strips, they may have slightly different ground potentials. This difference drives a current around the "loop" formed by the equipment connections, inducing interference into the audio signal.

Unbalanced cables near power cables: Unbalanced audio cables (standard 1/4-inch TS connectors, RCA cables) are susceptible to electromagnetic pickup from nearby power cables, transformers, and electrical equipment. Running an unbalanced mic cable next to a power extension cord picks up hum.

Poor quality equipment: Some consumer-grade audio equipment has inadequate electromagnetic shielding and introduces hum from internal components.

Fluorescent lighting: Fluorescent tubes and their ballasts produce electromagnetic interference that audio equipment can pick up. Particularly problematic in venues and offices.

HVAC and building electrical systems: Large HVAC transformers and electrical distribution equipment in buildings can induce hum in nearby audio systems.

Dimmer switches: Light dimmers create significant electromagnetic interference across a wide frequency range.

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Identifying Hum Before Removing It

Before applying any fix, identify the exact frequency:

1. Open the recording in any audio editor with spectrum analysis
2. Look at the frequency spectrum with no one speaking (just the hum)
3. Find the peak at the lowest frequency — this is the fundamental
4. Is it at approximately 50Hz or 60Hz?

If it's 50Hz: You're in a 50Hz power country. Your hum harmonics are at 100, 150, 200, 250Hz...

If it's 60Hz: You're in a 60Hz power country. Your hum harmonics are at 120, 180, 240, 300Hz...

If it's at neither: Could be a different interference source. Check for multiples of 50 or 60 — some interference manifests more strongly at harmonics than fundamentals.

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Method 1: Audacity Notch Filter (Free)

Audacity's Filter Curve EQ can apply notch filters at specific frequencies.

Steps:

1. Open your recording in Audacity
2. Go to Effects → Filter Curve EQ (or Equalization in older versions)
3. Add deep narrow cuts (notches) at:
   • 50Hz (or 60Hz) — the fundamental
   • 100Hz (or 120Hz) — second harmonic
   • 150Hz (or 180Hz) — third harmonic
   • Continue until the cuts have no audible effect

Settings for each notch:

• Frequency: the target harmonic
• Width (Q): narrow — you want to cut only the interference, not surrounding frequencies
• Depth: -30 to -40dB is usually sufficient

Audacity's dedicated Hum Removal: In newer versions of Audacity, Effects → Noise Removal and Repair → Hum Removal offers a simpler interface for targeting 50Hz or 60Hz hum with harmonics.

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Method 2: iZotope RX De-hum (Best Results)

iZotope RX's De-hum module is the most effective tool for hum removal. It:

• Identifies the fundamental frequency automatically
• Applies adaptive notch filters that track frequency variations (hum isn't always perfectly stable)
• Handles harmonics automatically up to the specified order

Settings:

• Fundamental frequency: Set to 50Hz or 60Hz based on your power system
• Number of harmonics: Start at 8. Increase if residual hum remains at higher frequencies.
• Reduction amount: Start at 20–30dB. Increase if the hum is still audible.

Preview and adjust: Listen to the result before applying. Excessive reduction can thin out the sound in the 50–100Hz range. Find the minimum reduction that makes the hum inaudible.

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Method 3: EQ Plugins in Your DAW

Most DAW EQ plugins (Fabfilter Pro-Q, Waves SSL E-Channel, Logic Pro Channel EQ, etc.) can apply notch filters manually:

1. Add the EQ plugin to your audio track
2. Create a band with a bell/notch type, very narrow Q
3. Set to the fundamental frequency (50 or 60Hz)
4. Pull down until the hum is eliminated
5. Duplicate for each significant harmonic

This is more tedious than a dedicated de-hum tool but achieves the same result.

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Method 4: Preventing Hum at the Source

For ongoing recording, prevention is better than cure:

Balanced cables and connections: XLR cables and balanced connections use a differential signaling method that cancels electromagnetic interference. Use balanced connections throughout your signal chain wherever possible.

Separate power sources: If ground loops are the problem, try running audio equipment from the same power strip/outlet. This eliminates ground potential differences.

Ground lift adapters: A DI box with a ground lift switch can break a ground loop between two pieces of equipment. Available for $20–50 at any music store.

Move cables: Keep audio cables away from power cables. If they must cross, cross at 90 degrees (perpendicular) rather than running parallel.

Replace fluorescent lighting: In recording spaces, replace fluorescent tubes with LED lighting. LEDs produce far less electromagnetic interference.

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What About Buzz (vs. Hum)?

"Buzz" typically refers to hum with prominent high-frequency harmonics that give it a more grating, complex character — it sounds buzzier and harsher than a simple tone.

Buzz often means:

• More harmonics are present and audible
• The fundamental may be at an odd frequency related to specific equipment
• Dimmer interference often sounds buzzier than ground loop hum

Treatment is the same — notch filtering at the fundamental and harmonics — but you may need more harmonics and broader notch widths to address buzz compared to clean hum.

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Special Case: Hum in Old Recordings

Old recordings (cassette, reel-to-reel, vinyl transfers) often have hum from the original recording or playback equipment. The same de-hum principles apply, but:

• The hum may have been recorded at a specific frequency that doesn't match your current power grid (if the recording was made in a different country)
• Recording equipment hum may be at non-standard frequencies
• Identifying the exact fundamental requires careful spectrum analysis

iZotope RX's De-hum can be set to a specific measured frequency rather than defaulting to 50 or 60Hz — use this for recordings where the hum is at an unusual frequency.

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When Professional Hum Removal Is the Right Call

For most recordings, hum removal is straightforward and DIY tools handle it well. Professional services add value when:

• The hum is severe and intermodulated with the wanted signal (making clean removal harder)
• Hum appears throughout a large archive of recordings needing consistent treatment
• The recording has other problems alongside hum that need professional attention
• The hum is at an unusual frequency that requires careful identification

WefixSound handles hum and buzz removal as part of comprehensive audio restoration. Upload your recording for a free 60-second sample showing the result before payment.

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Quick Reference: Hum Removal

Your country	Fundamental	Key harmonics
USA, Canada, Mexico	60Hz	120, 180, 240, 300Hz
UK, Europe, Australia	50Hz	100, 150, 200, 250Hz
Japan	50Hz (east) or 60Hz (west)	varies by region

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