Clean a podcast

This walkthrough takes a raw spoken-word recording with mains hum and background hiss to a clean episode at podcast loudness. Every command was run against ferraus 0.1.0 on a test recording; the outputs shown are trimmed copies of what it printed.

You need: ferraus, a recording (episode.wav here; any format ferraus reads works), and headphones. No models or downloads are needed for steps 1 to 6.

Making a test file. If you want to follow along without your own recording, this builds one: speech (macOS say; any voice recording works), pink hiss, and 60 Hz hum.

say -o speech.aiff "Welcome back to the show. Today we are talking about home recording."
ferraus convert speech.aiff -o voice.wav --sample-rate 48000
ferraus silence pad voice.wav --start 1.5s -o voice-pad.wav       # room tone before the first word
ferraus generate noise --color pink --dur 13.5s --amplitude -48dB --sample-rate 48000 -o hiss.wav
ferraus generate tone --freq 60Hz --dur 13.5s --amplitude -36dB --sample-rate 48000 -o hum.wav
ferraus mix voice-pad.wav hiss.wav hum.wav -o episode.wav

1. Listen, then ask ferraus what is wrong

Play the first ten seconds. Listen for: a low buzz under everything (hum), a steady "shhh" in the pauses (hiss), and level jumps between sentences.

ferraus analyze problems episode.wav

{
  "clean": false,
  "counts": {"high": 0, "medium": 2, "low": 1},
  "problems": [
    {"problem": "hum", "severity": "medium",
     "details": "60 Hz hum (harmonics [1]) at -23.1 dB relative to the signal",
     "suggested_fix": "dehum:freq=60Hz"},
    {"problem": "hiss", "severity": "medium",
     "details": "high-frequency noise floor of -57.7 dBFS (6–16 kHz) in quiet passages",
     "suggested_fix": "dehiss"},
    {"problem": "sibilance", "severity": "low",
     "details": "6% of loud frames are dominated by 5-10 kHz energy (peak -16.5 dBFS)",
     "suggested_fix": "deess"}
  ]
}

Every suggested_fix is an fx stage you can paste into a chain. Also note the starting loudness so you can compare later:

ferraus analyze loudness episode.wav

{"integrated_lufs": -16.4262, "loudness_range_lu": 1.7741, "true_peak_dbtp": -1.8811, ...}

2. Remove the hum

ferraus dehum episode.wav -o 1-dehum.wav --json

{"ok": true, "command": "dehum", "params": {"freq": "60.001Hz", "harmonics": "8", "depth": "-40dB", ...},
 "metrics": {"freq_hz": 60.001, "hum_reduction_db": 16.7}, ...}

ferraus found the mains frequency itself (60.001 Hz; in Europe and most of Africa and Asia it will find 50 Hz). Listen for: the buzz is gone in the pauses, and the voice has not lost its body. If a deep voice sounds thin, reduce the number of notched harmonics: --harmonics 4. To hear exactly what was removed, add --residual hum-only.wav.

3. Remove the hiss

Noise reduction works best when ferraus learns what the noise sounds like from a stretch that contains only noise. Most recordings have a second or two of room tone before the first word; --auto finds the quietest steady second for you.

ferraus denoise profile 1-dehum.wav --auto -o room.noiseprof --json

{"ok": true, "command": "denoise profile",
 "params": {"noise_region": {"range": "0.331s..1.323s", "level_db": -73.1, "method": "auto"}, ...},
 "result": {"profile": "room.noiseprof", "fft_size": 2048, "mean_level_db": -81.2, ...}}

Check that noise_region really is a pause (play that range). If it landed on a word, give the region yourself: --range 0s..1.2s. Then apply the profile and keep what was removed:

ferraus denoise 1-dehum.wav --profile room.noiseprof -o 2-denoised.wav --residual 2-removed.wav --json

{"ok": true, "command": "denoise",
 "metrics": {"mean_gain_db": -7.1, "input_rms_dbfs": -17.4, "output_rms_dbfs": -17.4, "removed_rms_dbfs": -53.3}, ...}

Listen for: the pauses are quiet, and there is no "underwater" or chirping sound on the voice (that sound is called musical noise). Then play 2-removed.wav: it should be hiss only. If you can hear words in it, the reduction is too strong; lower it with --reduction 8dB or raise --artifact-control 70%. If hiss remains, raise --reduction 18dB.

For a recording with no clean pause, or a changing background (traffic, a fan that speeds up), use a speech model instead of a profile:

ferraus denoise episode.wav --mode ml --model rnnoise -o clean.wav    # built in, no download
ferraus denoise episode.wav --mode ml -y -o clean.wav                  # DeepFilterNet 3, 8 MB download once

4. Polish the voice

enhance-voice is a preset chain for speech: a rumble filter, a de-plosive for p and b pops, a de-esser, gentle compression, and a presence lift. Pick male, female, or music.

ferraus enhance-voice 2-denoised.wav --mode female -o 3-voice.wav --json

{"metrics": {"stages": [
  {"op": "highpass", "args": {"freq_hz": 100.0, "order": 4}},
  {"op": "de-plosive", "args": {"below_hz": 150, "ducked_ms": 0.0}},
  {"op": "deess", "args": {"center": "7kHz", "threshold": "-24dB"}},
  {"op": "compress", "args": {"threshold": "-20dB", "ratio": "3:1", "attack": "5ms", "release": "80ms"}},
  {"op": "eq", "args": {"band": ["peak:250Hz:-1dB:q=1", "peak:4kHz:+2dB:q=1", "highshelf:12kHz:+2dB"]}}]}}

Listen for: clearer consonants, softer "s" sounds, and no boom on plosives. If it sounds too processed, blend it back: --mix 60%.

5. Even out the level, then set the loudness

Process the last steps in one fx pass. Each separate command writes an integer WAV file, and a stage that adds gain (the leveler does) can push peaks past full scale and clip in the file it writes. Inside one fx run the audio stays in floating point until the final normalize, whose limiter catches the peaks.

ferraus fx 3-voice.wav -o episode.clean.wav --fx leveler --fx "normalize:lufs=-16" --json

leveler raises quiet sentences and lowers loud ones slowly, like a careful engineer riding a fader. normalize --lufs -16 sets the integrated loudness to -16 LUFS (the usual target for stereo podcasts; the podcast spec for mono is -19 LUFS, see Loudness standards) and limits true peaks to -1 dBTP.

Listen for: every sentence at a similar level, with no pumping (the background swelling in the pauses). If the pauses get noisy, the leveler is boosting room tone: raise its noise gate, --fx "leveler:gate=-50dB".

6. Check the result

ferraus analyze problems episode.clean.wav
ferraus analyze loudness episode.clean.wav

{"clean": true, "counts": {"high": 0, "medium": 0, "low": 2}, ...}
{"integrated_lufs": -16.0249, "loudness_range_lu": 1.1295, "true_peak_dbtp": -1.0191, ...}

The whole thing in one command

Once you know the settings that suit your room, run every stage in one pass (the fx stage names and keys are the command names and flags):

ferraus fx episode.wav -o episode.clean.wav \
  --fx dehum --fx "denoise:auto" --fx leveler --fx "enhance-voice:mode=female" --fx "normalize:lufs=-16"

To trim long pauses as well, add ferraus silence trim episode.clean.wav --all --threshold -50dB --max-gap 700ms -o tight.wav. Choose the threshold from ferraus silence detect: it should sit a few dB above the floor level that command reports for the pauses.

For a whole folder of episodes, see the batch podcast cleanup recipe.

Reference

analyze problems · dehum · denoise profile · denoise · enhance-voice · leveler · normalize · fx · silence trim