A little know-how
Every file as loud as the next.
What LUFS and true peak are, which loudness to choose for Spotify, podcasts or broadcast, and how to normalize many audio files at once in your browser, without clipping. Nothing is uploaded.
By KeepSimp 5 min read
Play a playlist of files from different places and the volume jumps from one to the next. Turning the quiet ones up by their highest peak does not help: how loud a sound seems depends on all of it, not on its loudest moment. Loudness normalization measures what people hear and brings every file to the same figure.
LUFS: loudness as people hear it.
ITU-R BS.1770 measures loudness the way the ear weighs sound: it filters out the lowest bass, lifts the treble a little, averages the energy over 400 ms blocks and leaves out the silences and the very quiet parts. The result is in LUFS (loudness units relative to full scale), and a file at −14 LUFS sounds as loud as another at −14.
True peak is the highest the wave reaches, between the samples too, in dBTP. A file can have every sample under full scale and still clip when it is played or encoded, because the wave rises between them.
Which loudness to choose.
Spotify plays music at about −14 LUFS and turns louder tracks down to it. Apple asks for podcasts at about −16 LUFS, with true peaks no higher than −1 dB. European broadcasters use −23 LUFS (EBU R 128), and US television −24 (ATSC A/85). For your own playlists, any figure works as long as every file has the same.
How to normalize.
Open Normalize audio, drop your files and choose a loudness. Each file is measured as it will be written, made louder or quieter to reach the target, and a limiter keeps its true peaks under the ceiling, −1 dBTP unless you choose another. The file written is measured again, and the page says what it reached.
When a quiet file must be made much louder, the limiter lowers its loudest moments; if the ceiling keeps it from the target, the page says how loud it got rather than letting it clip.
On your device.
Files are read, measured and written in your browser and never uploaded. There is no account and no limit on how many you normalize.
Further reading
Topics: normalize audio · loudness normalization · LUFS · -14 LUFS · podcast loudness -16 LUFS · EBU R128 · true peak · normalize mp3 volume
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