Free Online Downmixer
Reduce channels: stereo to mono, or upmix mono to stereo.
What is this tool
AudioToolKit downmixes audio online for free, in your browser. Convert a stereo file to mono by averaging both channels into one — which also reveals phase problems as lost content — or upmix a mono track to stereo by duplicating it to both channels. The result downloads as MP3 or WAV, and the file is processed entirely on your device, never uploaded.
Drag and drop your files here
or
MP3, WAV, M4A, AAC, OGG, FLAC, AIFF, AIF, OPUS, WMA, AMR — up to 25 MB per file
Output
Mono or stereo MP3/WAV
Accepted formats
.mp3, .wav, .m4a, .aac, .ogg, .flac, .aiff, .aif, .opus, .wma, .amr
Why use this free tool
Radio, phones and old hardware often play mono. Downmixing to a single channel checks how a mix translates, and upmixing a mono file gives it a stereo bed for modern players.
How does the free downmixer work?
- 1
Upload the file.
- 2
Pick mono or stereo as the target.
- 3
Press Process and download.
Frequently asked questions
How does stereo to mono work?
Both channels are averaged into one, which also reveals phase problems as lost content.
Can I upmix mono to stereo?
Yes — the mono signal is duplicated to both channels. It is a real stereo file, not a widened one.
Local processing?
Yes, in your browser.
Related tools
More answers in the Help Center.