Free MP3 compressor that runs in your browser

What an audio converter actually does

Converting audio is two steps, not one. The file is decoded back to raw samples, then re-encoded into the format you asked for. Nothing is “translated” directly, which is why the order you convert in matters more than most converter pages admit.

Every lossy encode throws data away permanently. If you convert an MP3 into another MP3, the decoder reconstructs an approximation of the original and the encoder then discards detail from that approximation. The result is worse than either would have been alone. Convert from the best copy you hold — the WAV, the FLAC, the original recording — and go to your lossy format once, at the end.

Going the other way is safe but does not undo anything. Turning a 128 kbps MP3 into a WAV gives you an uncompressed file of a damaged signal: ten times the size, not a scrap more detail.

Which output format to pick

For bitrate, 192 kbps is the sensible default for music and 128 kbps is usually enough for speech. 320 kbps roughly doubles the file against 192 for a difference most people cannot hear on most material — and it cannot add back anything the source had already lost.

Using it as an MP3 compressor

If the file is already an MP3 and the only problem is its size, do not change the format — keep MP3 and lower the bitrate. MP3 bitrate is a flat rate in kilobits per second, so the result is arithmetic rather than a gamble, and you can work out the new size before you press Convert:

Dropping a 320 kbps file to 128 kbps takes it to 40 per cent of its size. Whether you can hear the difference depends on the material and on what you are playing it through — speech and podcast dialogue survive 128 kbps comfortably, dense music is where it starts to show.

A note on the word, because it has two meanings in audio. Compressing a file and compressing a signal are unrelated jobs. A dynamic-range compressor evens out loud and quiet passages and changes how the audio sounds; that is not what this does. This makes the file smaller and leaves the dynamics where they were.

The one-way rule from the section above still applies. Re-encoding at a lower bitrate discards detail for good, so compress from the best copy you have and keep that original — converting the 128 kbps result back up to 320 kbps restores nothing and simply makes the file large again.

How to convert an audio file

1. Drop the file in. Anything the local engine can decode works, including formats your browser alone cannot open, such as WMA and ALAC.
2. Choose the output. Format first, then bitrate if you picked MP3 or AAC. Sample rate and channels can stay on Same as source unless something downstream requires otherwise — 48 000 Hz for video, mono for a voice track.
3. Press Convert, then download. The first run also fetches the audio filter engine, about 2 MB; after that it is cached and every later conversion starts straight away.

Why it matters that this runs locally

Most free converters take your file to a server, convert it there, and hand back a link. That means an upload, a queue, and a copy of your audio on a machine you do not control — which is a real consideration for an unreleased track, a client interview or a recording of someone who did not agree to be uploaded anywhere.

Audiofilter inverts it: the converter is downloaded to you, and the audio never moves. You can check that claim in about ten seconds — open the browser's network panel, convert something, and read the list. Every request is a download of the engine from this site, and there is no request carrying your file the other way. We wrote up what each Audiofilter tool downloads and how to run that check in more detail.

What this converter will not do

• No FLAC or OGG output. The engine in your browser can read both, but it carries encoders for MP3, AAC and 16-bit WAV only. Adding more would mean a larger download for every visitor, including the ones who never need them.
• WAV comes out as 16-bit. Fine for delivery and for most editing; not the choice for a mastering chain that wants 24-bit or float.
• Tags and cover art are not carried across. The converter strips embedded artwork, because the WAV and AAC containers here cannot hold it. Re-tag afterwards if it matters.
• One file at a time. There is no batch queue yet. The engine stays loaded between runs, so files go through quickly one after another.
• It converts, it does not edit. For taking noise out of a recording or pulling a vocal off a track, use the tools below.

The rest of the Audiofilter audio filter set

The converter shares its engine and its no-upload design with four other tools on this site. All of them run in the browser tab, and all of them are free with no account.

• AI vocal remover — split a song into an isolated acapella and a karaoke-ready instrumental.
• AI noise reducer — the audio filter for fan hum, air conditioning and mic hiss sitting behind speech.
• AI text to speech — 19 voices, plus cloning from a short sample that stays on your device.