Removing Background Noise from Audio Recordings

Types of Background Noise

Background noise falls into two categories: stationary noise (consistent hum, hiss, fan noise) and non-stationary noise (traffic, voices, clicks). Stationary noise is easier to remove because its frequency profile is predictable. Non-stationary noise requires more sophisticated techniques.

Noise Gate Basics

A noise gate silences audio below a threshold, effectively muting quiet sections where noise is most audible. Set the threshold just above the noise floor. Use a fast attack (1-5ms) so speech isn't clipped, and a medium release (50-200ms) to avoid choppy cutoffs. Noise gates don't remove noise during speech — they only silence pauses.

Spectral Noise Reduction

For removing noise that's present even during speech, spectral noise reduction analyzes a noise profile (a sample of pure noise) and subtracts those frequencies from the entire recording. Capture at least 2 seconds of room noise before recording. Apply reduction conservatively — aggressive settings create underwater-sounding artifacts.

Dealing with Specific Noise Types

For 50/60 Hz hum (electrical interference), use a notch filter at the fundamental frequency and its harmonics (120 Hz, 180 Hz, etc.). For air conditioning rumble, apply a high-pass filter at 100-150 Hz. For computer fan noise, spectral reduction works well since fans produce consistent broadband noise. For mouth clicks, use a de-clicker plugin or manually edit them out.

Prevention Over Cure

The best noise removal happens before recording. Use a dynamic microphone in noisy environments (they reject more room noise than condensers). Position the mic close to the source (6-12 inches). Turn off unnecessary electronics. Record during quiet hours. A $20 moving blanket draped over a frame reduces room reflections dramatically.