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# Denoise audio with afftdn
- URL: https://ffmpeguru.com/denoise-audio-with-afftdn/
- Published: 2026-09-03T09:00:00.000Z
- Updated: 2026-10-13T17:59:42.000Z
- Author: FFmpeguru
- Tags: ffmpeg

Afftdn is a frequency-domain denoiser for audio. It computes a short-time Fourier transform, identifies the noise floor in each frequency bin, and subtracts it. The result is a clean signal with the speech or music preserved, useful for field recordings, voice memos, and old tapes.

## The command

```
ffmpeg -i noisy.wav -af "afftdn=nf=-25" clean.wav
```

## What it does

The \`afftdn\` filter takes a noise floor in dB. Set the value to the RMS level of the noise you want to remove; a typical value for office hum is -40 dB, for traffic noise -30 dB. The filter learns the noise profile from the first 0.5 seconds of the file by default, so start the input with a known-silent section. The output is a single-pass denoised file.

## Requirements

Any audio input. The filter is in libavfilter. CPU-only — the FFT is not cheap on long files, so budget for a one-time cost. The filter is mono by default; for stereo, pass \`afftdn=nf=-25:channels=stereo\` or run two instances.

## Things to avoid

- Setting the noise floor too high. A value of -10 dB will cut not just the noise but also the speech, leaving a hollow-sounding file.
- Running afftdn on a file with no silent intro. The filter needs a sample of the noise floor to learn; if the file starts with speech, it will treat the speech as noise and remove it.
- Confusing afftdn with the \`anlmdn\` filter. anlmdn is a non-local means denoiser; it preserves transients better but is much slower. Use afftdn for steady-state noise (hum, hiss); use anlmdn for transient noise (clicks, pops).
- Applying denoise to the entire file. For a music track with a long quiet intro, the filter may erase the room tone. Trim the file first if the noise is concentrated in a section.