# AudioMaster LUFS — User Guide

**Mergify Digital · Free tool (standalone download)**

## What it is

AudioMaster LUFS masters audio to a loudness target using FFmpeg's `loudnorm` filter in a measured two-pass process: the first pass measures your audio's integrated loudness, true peak, and loudness range; the second pass applies loudness normalization using those measurements, and the finished file is re-measured so the result you get back is a measured value, not an estimate. It runs entirely on your own computer — no uploads, no account.

- **Input:** WAV, MP3, M4A, FLAC, OGG (AAC also accepted)
- **Limits:** up to **200 MB** per file and up to **30 minutes** long
- **Output:** 16-bit PCM WAV at 48 kHz
- **True-peak ceiling:** −1 dBTP on every master

## Loudness targets

| Target | Integrated loudness | Typical use |
|---|---|---|
| Spotify | −14 LUFS | Spotify and most music streaming |
| YouTube | −14 LUFS | YouTube uploads |
| Apple | −16 LUFS | Apple Music / Apple Podcasts loudness |
| Podcast | −16 LUFS | Spoken-word podcast distribution |
| Custom | any value from −36 to −5 LUFS | Anything else — you set the number |

## Requirements

- The free AudioMaster LUFS download (ZIP) from the Mergify Digital free tools section
- Python 3.10 or newer
- FFmpeg installed and on your PATH (`ffmpeg -version` should print a version banner)
- An audio file in one of the supported formats, within the size/duration limits above
- Optional: the included `app.py` web UI needs the packages in `requirements.txt` (FastAPI/Uvicorn); the command-line tool needs nothing beyond Python + FFmpeg

## Getting started

1. **Download and unzip.** Get the free ZIP from the free tools section of the Mergify Digital site and unzip it anywhere.
2. **Install FFmpeg** if you don't have it (ffmpeg.org or your OS package manager), and confirm `ffmpeg -version` works in a terminal.
3. **Master a test file first.** Run one track at the Spotify target and listen to the result before processing a full release:

```
python cli.py my-track.mp3 my-track-mastered.wav --target spotify
```

`--target` accepts `spotify` / `youtube` (−14 LUFS), `apple` / `podcast` (−16 LUFS), or any custom LUFS number from −36 to −5. The tool prints a JSON summary with the measured output loudness and true peak when it finishes.

## Step-by-step: master a track

1. **Prepare your mix.** Master from the best-quality source you have — an unmastered WAV or FLAC mix, not an MP3 of an MP3. Loudness processing cannot restore quality lost earlier.
2. **Choose a target.** Pick the preset for where the audio is going (Spotify/YouTube −14, Apple/Podcast −16), or pass a custom LUFS value between −36 and −5.
3. **Run the tool.** AudioMaster measures your file (pass 1), applies loudnorm with the measured values (pass 2 — linear mode when the required gain keeps the true peak under the −1 dBTP ceiling, dynamic mode when it cannot), and re-measures the output.
4. **Check the printed measurements.** The JSON summary reports the measured output loudness and true peak. In verification testing, outputs landed within 0.05 LUFS of target on representative files; treat ±1 LUFS as the honest working tolerance for difficult material.
5. **Listen before you ship.** Play the mastered WAV start to finish. Loudness-correct is not the same as sounds-right — if the mix itself is harsh or muddy, fix the mix and re-master.

## Tips

- Leave headroom in your mix: a mix slammed to 0 dBFS gives the normalizer nothing clean to work with.
- One target per destination — a −14 music master and a −16 podcast master are different files; keep both, labeled.
- Very dynamic or very quiet material may be processed in dynamic mode, which trades a little target precision for peak safety. That trade is deliberate.
- Keep your unmastered mix archived. Targets change; platforms change their loudness policies.

## Troubleshooting

- **"FFmpeg not found" / the tool fails immediately.** FFmpeg isn't installed or isn't on your PATH. Install it, open a fresh terminal, and confirm `ffmpeg -version` works.
- **"Unsupported format" error.** Convert the file to WAV, MP3, M4A, FLAC, or OGG and retry.
- **File rejected as too large or too long.** Files over 200 MB or longer than 30 minutes are refused. Split long recordings into parts under 30 minutes.
- **Output loudness is off target.** Check the printed measurement first — quiet intros and long silences pull integrated loudness down. Trim silence, fix the mix balance, and re-run.
- **Master sounds squashed.** Your source was probably already heavily limited. Re-export the mix with less bus compression and master again.

## Support

Email: **support@mergifystudios.com**

Website: https://mergifydigital.mergifystudios.com

Please include: "AudioMaster LUFS", the target you selected, your operating system, and a short description of the problem. Do not send passwords or full payment-card numbers.

## Disclaimer

AudioMaster LUFS is an audio loudness-processing utility provided as-is. It normalizes loudness to the target you select; it does not guarantee acceptance by any streaming platform, broadcaster, or distributor — platforms apply their own measurement and playback normalization, and their policies change. You are responsible for the rights to any audio you process and for listening to and approving the mastered file before release.