Make an MP3 louder

What the numbers mean

Loudness is measured in LUFS, the scale Spotify, Apple Music and YouTube use to level tracks against each other. Spotify plays at about −14 LUFS; a voice memo or an old CD rip often sits at −20 to −25, which is why it sounds so much quieter next to everything else.

Loudest peak is the highest single sample in the file. The gap between it and the ceiling is how much you can raise the file for free. If it says −8 dB, the first 7 dB of boost change nothing but the level; anything beyond that is the limiter working.

Normalise or boost?

For a file you are going to share, or one that has to sit in a playlist next to normal-level tracks, normalise. It measures first and lifts by exactly what the file needs, so a whisper-quiet lecture gets a large lift and a song that is already loud gets almost none. Pick Speech for podcasts and audiobooks, Music to match streaming services, or Loud when it has to cut through a noisy room.

A fixed boost is for when you already know the number — "this album is about 6 dB too quiet". Either way the limiter is on, so the result cannot clip.

Why a limiter, and when it starts to show

Raise a file past its loudest peak and those peaks have nowhere to go: they flatten against the ceiling and you hear crackle. A limiter turns the level down for just those few milliseconds, a fraction of a second before the peak arrives, so everything else can keep rising. For a few decibels it is inaudible. Push 10 dB or more past the clean room and drums start to lose their snap — the tool tells you when you are in that territory.

Quality: what changes and what does not

Changing the level means decoding the MP3 and encoding it again, and every MP3 encode throws a little detail away. That is why the tool matches your original bitrate rather than defaulting to something lower: a 320 kbps file comes back at 320. If you need a change with no re-encode at all, MP3Gain-style tools edit the gain value inside the file in 1.5 dB steps — how to make an MP3 louder compares every method, including the ffmpeg commands.

If you only want to hear it louder

Making a new file is the right answer when you will send it to someone or play it on something else. If the goal is just to listen to quiet files at a sensible level on your phone, you do not need a copy at all: Volume Booster plays your audio with gain, a bass booster, a 6-band equalizer and a limiter applied as it plays. To try those equalizer settings on a file first, the online equalizer runs the same six bands in your browser. For a quiet video rather than a song, use make video louder.