Free tool

Audio Compressor: Reduce Audio File Size

Shrink an audio file to fit an email, a chat app or an upload form. Choose a target bitrate and, for voice recordings, mono; the tool shows the estimated size before you start, then compresses the file in your browser without uploading it.

01 — Your file

Choose a file

02 — Result

Your converted file

Choose a file and press Compress. The conversion runs in this tab, so even large files never leave your computer or phone.

How to make an audio file smaller

  1. Open the recording with the box above. Video files work too; only the sound is kept.
  2. Choose MP3 for maximum compatibility, or M4A for slightly better sound at the same size.
  3. Pick a target bitrate. The estimated result appears under the settings.
  4. For a single voice, tick Mono. Then compress and download.

Choosing the bitrate

The bitrate alone decides the size of the result, whatever the original was:

128 kbps
about 58 MB per hour. Music still sounds good.
96 kbps
about 43 MB per hour.
64 kbps
about 29 MB per hour. Speech remains clear, especially in mono.
48 kbps
about 22 MB per hour. Fine for lectures and meetings in mono.
32 kbps
about 14 MB per hour. Speech stays understandable; music suffers.

The estimate under the settings compares the result with the current size, so you can try a setting before committing to it. A WAV shrinks far more dramatically, because it started uncompressed: an hour of CD-quality WAV is over 600 MB.

Why mono helps for voice

A recording of one person talking carries the same sound in both channels. Mixing it to mono lets the encoder spend all of its bitrate on one channel, so 64 kbps mono sounds noticeably better than 64 kbps stereo. Keep stereo for music, and for interviews where two people were deliberately recorded on separate channels.

This is file compression, not a dynamics compressor

In audio production, "compressor" also means an effect that evens out loud and quiet passages. This tool doesn't change the loudness; it reduces the amount of data. If your recording has some very quiet and some very loud parts, the dynamic range compression article explains how to fix that in an editor.

Smaller files for transcription

Speech recognition copes well with compressed audio: for clear speech, a 64 kbps mono MP3 keeps the words intact and uploads in a fraction of the time. Compress a long recording here, then send it to mydubly's audio to text tool. The audio bitrate for speech recognition article covers how low you can safely go.

How the free converter works

The converter is ffmpeg, the open-source media toolkit, compiled to WebAssembly so it runs inside your browser tab. Your file is read straight from your disk by that engine; it is never uploaded to mydubly or anywhere else, and no account is needed.

  • The engine is about 30 MB and downloads the first time you convert something. After that your browser normally keeps it.
  • Large inputs are fine because the file is read in place, but the result is built in memory, so outputs are capped at about 1.5 GB.
  • Speed depends on your device. Copying streams takes seconds; re-encoding video is the slow case.
  • Keep the tab open until the download button appears. Closing it stops the conversion.

More free tools

Turn the file into text

Frequently asked questions

How can I reduce the size of an audio file without losing quality?

Some loss is unavoidable with lossy compression, but for speech 64 kbps mono is hard to tell apart from the original. For music, 128 kbps keeps most of the quality.

How do I compress an MP3 to send by email?

Open it here, choose a lower bitrate such as 64 kbps, tick Mono if it's speech, and compress. The estimate shows the size before you start.

Can I compress a WAV file?

Yes. Converting WAV to 128 kbps MP3 makes it roughly eleven times smaller; lower bitrates shrink it further.

Does it change the volume of my recording?

No. It reduces data, not loudness. Dynamic range compression is a different effect applied in an audio editor.