Question 1

How does Audacity's Noise Reduction effect actually work?

Accepted Answer

Audacity's Noise Reduction uses a two-pass spectral subtraction method. First pass: you select a region of 'silence' (noise only, no speech), then click 'Get Noise Profile' — Audacity captures the frequency spectrum of just the noise. Second pass: Audacity subtracts that noise spectrum from the entire track, attenuating frequencies that match the profile. The Noise Reduction slider (dB) controls how aggressively noise is cut; Sensitivity controls how confidently Audacity identifies noise vs. speech; Frequency Smoothing blends adjacent frequency bands to reduce musical noise artifacts. The limitation is that the noise profile is static — if your noise changes during recording (like an AC cycling), the subtraction becomes inaccurate.

Question 2

Why does my voice sound metallic or robotic after Audacity noise reduction?

Accepted Answer

The metallic/robotic sound (also called 'musical noise') happens when Audacity's Sensitivity is set too high or Noise Reduction dB is too aggressive. At these settings, Audacity erroneously identifies parts of your voice as 'noise' and attenuates them, creating discontinuous spectral dropouts that produce the characteristic artifact. Fix: reduce Noise Reduction from the default 12 dB down to 6-9 dB, and lower Sensitivity from the default 6 toward 3-4. Alternatively, increase Frequency Smoothing from 3 to 5-6 bands to reduce the sharp spectral discontinuities that cause the metallic sound.

Question 3

What's the best noise profile length to capture in Audacity?

Accepted Answer

Capture at least 0.5 to 1 second of pure noise — no speech, clicks, or movement. Longer is better: 2-3 seconds gives Audacity a more statistically reliable spectrum of the noise floor. The noise sample should come from the same recording session as the speech, ideally immediately before you started speaking. Don't use noise samples from a different microphone position or room setup, as the frequency spectrum will differ. If your recording has no silent section, you can use a gate or noise floor from a different file recorded in the same conditions.

Question 4

Does Audacity's Noise Gate work differently from Noise Reduction?

Accepted Answer

Yes, fundamentally different. Audacity's Noise Gate (also called 'Gate') silences audio that falls below a defined amplitude threshold — it's a level-based tool, not frequency-based. When you stop speaking, the gate closes and cuts everything below the threshold dB level. This removes noise during pauses but does nothing to noise that overlaps with speech. Noise Reduction operates on the full recording, removing noise frequencies even while speech is present. For a quiet room with consistent noise, Noise Reduction is better. For a room with intermittent noise (phones, HVAC cycling), combining both — Noise Reduction first, then a light Gate for pauses — works well.

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