Why this is fast
Native server ffmpeg with real SIMD and threading runs the denoise + normalize chain roughly 4–8x faster than browser WebAssembly on the same audio. afftdn is a real-time-capable frequency-domain filter, so even a 60-minute podcast finishes in well under a minute of CPU time. Uploads land at the nearest Backblaze B2 point of presence via a presigned URL, the cleaned MP3 comes back through Bunny CDN from the same edge.
What this tool does, exactly
The filter chain is afftdn=nf=<floor>, highpass=f=80, lowpass=f=12000, loudnorm=I=-16:TP=-1.5:LRA=11 followed by LAME at VBR quality 2 (~190 kbps). afftdn is ffmpeg's adaptive frequency-domain denoiser — it estimates the noise floor and gates everything below it. The highpass at 80 Hz removes sub-bass rumble (HVAC, mic-stand thumps). The lowpass at 12 kHz drops ultrasonic fizz and high-frequency hiss. loudnorm targets the EBU R128 broadcast standard (-16 LUFS integrated, -1.5 dBTP, 11 LU range), so the output sits at a comfortable, consistent level.
How afftdn beats arnndn for one-shot cleanup
Two reasons. First, afftdn is bundled with ffmpeg and needs no model file — arnndn requires a trained RNNoise model (.rnnn) that has to ship with the binary, and the open models are tuned for specific noise profiles. Second, afftdn is adaptive: it estimates the noise floor from your file and gates frequencies below it, which works on whatever mix of hiss, hum, and fan whir your recording happens to contain. arnndn is better at heavy chaotic backgrounds when its model matches your noise, but when it does not the cleanup can sound spectrally strange. For the common case — a single voice over steady noise — afftdn at the Medium (-25 dB) noise floor is the right default.
Sister tools
Got noise inside a video, not a standalone audio file? Strip the soundtrack first with video to audio converter, clean it here, then mux the cleaned audio back over the video in an editor. Loudness is the only problem? Normalize video audio targets -16 LUFS without touching noise. Trim the cleaned MP3? MP3 cutter. Shrink it for email? Compress audio. Check the mic before the next recording to avoid the cleanup altogether? Microphone test online. Recording a fresh take in the browser? Voice recorder captures straight to MP3.