MP3 Volume Booster

Open the MP3 above. Auto measures it and turns it up to about −14 LUFS, the level of music on streaming services. Press Play to check it, move the slider if you want it louder or quieter, then press Save to download the louder MP3.

No clipping, at any setting: every boost goes through a limiter that keeps the peaks just under the top. If you push a file so far that the limiter has to hold its loud parts down by more than about 6 dB, which can start to sound squashed, a note appears with a button back to Auto.

For music, about −14 LUFS, the level music streaming services play at and the level Auto aims for. Podcasts usually sit around −16 LUFS and TV around −23. A song that is already louder than −14 LUFS gains little from more volume, because streaming services turn loud tracks down to that level anyway.

Open the recording, whether it is a voice memo, a voice message or a lecture. Auto lifts the voice to a clear level; very quiet recordings often get +20 dB or more. Bumps and claps are held back by the limiter, so the speech can come up without them crackling.

Yes. Open the video file, such as MP4, MOV or WebM, and its sound is measured and boosted like any audio file. Save gives you the louder soundtrack as MP3 or WAV, which you can put back under the video in your video editor.

MP3, WAV, M4A, AAC, FLAC and OGG audio, plus videos such as MP4, MOV and WebM. Each file can be up to 500 MB. The louder version is saved as MP3 (320 kbps) or WAV, at the same sample rate, channels and length as your file.

No. Your file is measured, boosted and saved in your browser, on your own device, and nothing is sent to a server. Reloading or closing the page clears it.

Yes. It works in Safari on iPhone and iPad, in Chrome on Android and in any current browser on a computer. Choose the file from your phone, drag the slider with your finger and press Save; the louder file goes to your downloads.

Open and save them one after another. Auto measures each file and brings the quiet ones to about −14 LUFS, so they end up at the same level. A file that is louder than the rest can be turned down with the slider until the readout shows about −14 LUFS.

LUFS stands for Loudness Units relative to Full Scale. It measures how loud a recording sounds over its whole length, weighted the way human hearing works, and it is the unit streaming services and broadcasters use to set levels. −14 LUFS is louder than −20 LUFS, and one LUFS step is the same size as one decibel.

Because it was already loud. Most finished songs measure −14 LUFS or louder and their peaks already reach the top, so Auto leaves them at 0 dB. You can still turn them up by hand: the limiter holds the peaks down, which makes the song denser rather than much louder, and past about 6 dB of limiting it starts to sound squashed.

The slider goes from −12 to +30 dB in half-dB steps, and every 10 dB sounds about twice as loud. Auto picks the gain for −14 LUFS: quiet voice recordings often need +15 to +25 dB, while most songs need little or none.

Yes. Open the louder file in the Pitch Changer to raise or lower its key or to play it faster or slower, then save it again.

Yes. Measuring, boosting and saving are free, with no account and no watermark, as often as you like.