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Glossary · metric

What is Audio normalization (LUFS, loudness)?

Audio normalization is the process of adjusting volume levels so all content plays at roughly the same loudness. YouTube's Stable Volume feature uses -14 LUFS (Loudness Units relative to Full Scale) as the target — videos louder than that get attenuated, quieter ones get amplified.

Also called:audio leveling · lufs · loudness · stable volume

LUFS is the modern measure of perceived loudness, replacing the older "peak level" metric. -14 LUFS is roughly "average TV broadcast loudness". -23 LUFS is broadcast standard in Europe. -8 LUFS is "loud" — music CDs from the loudness wars era.

YouTube normalizes uploaded audio to its target. A song mixed at -8 LUFS gets pulled down to -14 LUFS for playback (sounds quieter than the source intended). Mixing for YouTube: target -14 LUFS to avoid normalization changes; mix louder if you want bass-heavy content to feel impactful.

For downloaders: the audio bytes you download preserve YouTube's normalized output, not the uploader's original mix. If you specifically want "the loud version" of a music track, the YouTube version isn't the right source — get the original studio file or stream from a service that doesn't normalize as aggressively.

Common questions

Why does YouTube sound quieter than Spotify?
Different normalization targets. YouTube uses -14 LUFS; Spotify can go up to -11 LUFS for "normal" content. The 3 LUFS difference is audibly meaningful — perceptibly louder on Spotify at the same volume slider.

Related terms

Bitrate

Bitrate is the amount of data a video or audio stream carries per second, measured in bits per second (bps) or kilobits (kbps) and megabits (Mbps).

Audio channel (mono, stereo, 5.1, etc.)

An audio channel is a single track of sound that gets routed to a specific speaker.

M4A

M4A is an audio-only file format that wraps AAC-encoded audio in an MP4 container.

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