To check how loud a song is, run the whole file through a loudness meter that follows ITU-R BS.1770 and read its integrated loudness in LUFS, plus its true peak in dBTP. Those two numbers tell you how loud the track will sound next to other music and whether its peaks are safe once it's encoded for streaming. Peak level and waveform size don't tell you either.
Try SoundGen's free loudness meter: drop in a file and it measures integrated LUFS, true peak, sample peak and loudness range in your browser, then shows how much each streaming service would turn the track down, or up. Nothing is uploaded.
What LUFS measures
LUFS stands for Loudness Units relative to Full Scale. It's defined by the ITU's BS.1770 recommendation, and broadcasters use the same measurement under EBU R 128. One LU is one decibel, so a track at −10 LUFS is 4 dB louder than one at −14.
A peak meter only tells you the highest sample. LUFS tries to measure how loud the music sounds, in three steps:
- K-weighting. The signal is filtered first: a high-pass discounts deep bass, and a shelf lifts the upper range by about 4 dB, roughly following how the ear weights frequencies.
- Blocks. The weighted power is measured in 400 ms blocks that overlap by 75%, and the channels are added together.
- Gating. Blocks quieter than −70 LUFS are dropped, and so are blocks more than 10 LU below the average of what's left. Silence, fades and very quiet passages therefore don't drag the figure down.
The result is integrated loudness: one number for the whole song. Meters usually show more readings alongside it:
- Short-term (a 3 s window) and momentary (400 ms), which change as the song plays.
- Loudness range (LRA), from EBU Tech 3342, which measures how much the loudness moves over the song, in LU. A low LRA means the level hardly changes; a high one means quiet and loud sections far apart.
A quick check that a meter is calibrated: a full-scale 1 kHz sine in one channel reads −3.01 LUFS, and the same sine in both channels reads 0 LUFS.
True peak vs sample peak
The sample peak is the largest sample value in the file. But a converter rebuilds a continuous waveform between the samples, and that waveform can rise above the highest sample. A true-peak meter estimates it by oversampling (BS.1770 describes a 4× method) and reports it in dBTP.
This matters because lossy encoders (MP3, AAC, Ogg) change the waveform, and a master whose true peak sits right at 0 dBTP can clip after encoding. Spotify asks for masters to stay below −1 dBTP, and below −2 dBTP if they're louder than −14 LUFS.
How to check a song's loudness
- Use the final file. Measure the exported master, not the project with the master chain bypassed.
- Measure the whole song. Integrated loudness is defined over the full programme. Glancing at a meter while the chorus plays gives you short-term loudness, not integrated.
- Read integrated LUFS, true peak and LRA. The free loudness meter shows all of them for a WAV, MP3, M4A or FLAC.
- Compare like with like. To check against a reference track, measure the reference the same way. Commercial masters are often around −8 to −11 LUFS, well above the streaming references.
What streaming services do with the number
Most music streaming services apply loudness normalisation: they change the playback volume so tracks sit at roughly the same loudness. Your file isn't altered, and a louder master isn't rejected. It's just turned down.
Spotify publishes how it does this (Spotify for Artists: loudness normalization):
- The default Normal setting plays music at −14 LUFS. Premium listeners can choose Loud (−11) or Quiet (−19).
- Tracks louder than the reference are turned down.
- Quieter tracks are turned up, but only as far as their peaks allow, leaving 1 dB of headroom. Spotify's own example: a track at −20 LUFS with a true peak of −5 dB is raised only to −16 LUFS.
- The web player and third-party devices such as TVs and speakers don't apply normalisation.
Other services don't publish their figures in the same way. Engineers' measurements commonly put YouTube at about −14 LUFS (turning loud tracks down, not quiet ones up), Apple Music with Sound Check at about −16, and Amazon Music and Tidal at about −14. Treat these as approximate and subject to change.
Is my song loud enough for Spotify?
There's no "loud enough". A track at −8 LUFS is turned down 6 dB and plays at about the same level as a −14 LUFS track. What remains is the difference between the masters: the louder one has had its peaks limited harder to get there, so after normalisation it can sound flatter and less punchy. A track much quieter than −14 is raised only as far as its true peak allows, so a very dynamic master with high peaks may play a little quieter than the rest of a playlist.
A practical way to read your result:
- Around −14 LUFS, true peak at or below −1 dBTP: Spotify plays it at about the level you mastered it.
- Louder than −14: it will be turned down. That's fine if you like how the master sounds; keep the true peak at or below −2 dBTP.
- Much quieter than −14, with high peaks: it may play a little under other tracks on Spotify. Gentle limiting lowers the peaks and leaves room for normalisation to raise it.
Doing it in SoundGen
- Check a file: the free loudness meter runs the studio's own BS.1770 meter on your device.
- In the studio: the studio's Mastering panel shows integrated loudness and true peak live against a target, and the AI master renders the mix and masters it to a streaming target by measurement, with a true-peak limiter.
FAQ
What does LUFS stand for? Loudness Units relative to Full Scale, the loudness measure defined by ITU-R BS.1770. LKFS is the same measure under the ITU's name.
What LUFS should I master to for streaming? No level is required. Spotify normalises to −14 LUFS by default, so mastering much louder only gets turned down. Decide by how the master sounds, keep the true peak at or below −1 dBTP, and check what normalisation will do with the number.
Why does my DAW show a different number? Check that it's showing integrated loudness over the whole song, not short-term or momentary. Small differences also come from sample-rate conversion and different true-peak oversampling filters.
Does Spotify change my audio file? No. Normalisation changes playback volume, and listeners can switch it off. Spotify's Loud setting also applies a limiter to keep quiet, dynamic tracks from clipping when they're raised.
What's the difference between LUFS and dB? dBFS measures signal level, usually the peak. LUFS measures perceived loudness over time. A change of 1 LU is a change of 1 dB.
Sources
SoundGen Team
Written by the team building SoundGen
