FAQ

LUFster runs four analyses on a track, all in the browser:

• Loudness — integrated LUFS, true peak, loudness range, short-term max, peak-to-loudness ratio.
• Spectral balance— energy per frequency band and the spectral centroid (the “center of gravity” of the spectrum).
• Stereo width — width across the frequency spectrum and mono correlation, which tells you whether the mix collapses cleanly to mono.
• Energy timeline — how loud and how bright the track is across time.

LUFS (Loudness Units Full Scale) is the standard measurement for audio loudness used across broadcast and streaming platforms. Unlike peak measurements, LUFS accounts for human perception of loudness by applying psychoacoustic weighting.

It’s the unit streaming services use to normalize playback, and the reason a quiet track and a brick-walled track can sit at the same perceived level on Spotify.

EBU R128 is the European Broadcasting Union recommendation for loudness measurement. It builds on the ITU-R BS.1770 loudness algorithm and specifies how to measure integrated loudness, loudness range, and true peak. LUFster implements this standard.

Streaming:

• Spotify: -14 LUFS integrated
• Apple Music: -16 LUFS integrated
• YouTube: -14 LUFS integrated
• Amazon Music: -14 LUFS integrated

Broadcast:

• TV/Radio (EBU R128): -23 LUFS integrated

Other:

• Club/DJ: -9 to -13 LUFS (louder for club systems)
• Podcast: -16 to -20 LUFS

• Integrated: Average over the whole track. The number streaming platforms use.
• Short-term: 3-second sliding window. Useful for finding the loudest section.
• Momentary: 400ms sliding window. Catches very short-term spikes.

Mono correlation runs from -1 to +1.

• +1 — fully mono. Identical signals in both channels.
• ~+0.5 to +1 — mono-safe. Collapses cleanly to a single speaker.
• 0 — fully uncorrelated channels. Maximum width.
• Below 0 — channels partially out of phase. Parts of the mix may disappear on mono playback (clubs, phones, some smart speakers).