Mono / Stereo
Mono / Stereo converts a recording between one and two channels. Downmix a stereo file to mono for a smaller size and consistent playback on single-speaker devices, or turn a mono source into stereo. It's a quick, lossless-friendly conversion done entirely in your browser.
Add your audio file
The file is read by your browser and stays on your device — there is no upload step.
Your audio
The work runs in this tab. Nothing is sent anywhere, and the download is generated locally.
Output —Load audio
How to use Mono / Stereo
- 01Upload
Add your audio
Drop your file in and play it to hear the current channels.
- 02Customize
Choose mono or stereo
Pick Mono to downmix to a single channel, or Stereo to output two channels.
- 03Process
Download
Export to convert the channels and save the file.
What converting channels does
Folds two channels into one, or duplicates one into two. Stereo to mono sums the left and right; mono to stereo copies the same signal to both sides.
What does not change
Length, pitch and speed. Going to mono halves the data, which is the largest saving available on a spoken-word recording. Going the other way makes the file twice as large without adding any information — do it for compatibility, never for quality.
Supported formats
- MP3
- WAV
- M4A
- OGG
- FLAC
- Maximum file size —
- bounded by your device's memory
- Processed by —
- FFmpeg (WebAssembly), on your device
Your file, and what the page does
Your file is never uploaded. Mono / Stereo reads it into this browser tab and processes it with FFmpeg compiled to WebAssembly on your own device. There is no upload endpoint in the application and no copy on any server — closing the tab discards it.
That is also why processing takes longer here than on a site that uploads: your device is doing the work rather than a rack of servers. The trade is that the file never leaves it.
What the page does send or fetch
- The processing engine, once
- The first time you use any video or audio tool, the browser downloads the FFmpeg WebAssembly build (~30MB) from the jsDelivr CDN and reuses the cached copy afterwards. That is a file coming to you — no part of your own file is in the request.
- Ads on the page
- The site is funded by advertising, so the page loads Google AdSense. That carries the usual web basics — IP address, browser, referring page — as on any ad-supported site.
- An anonymous usage counter
- When Mono / Stereo finishes we record that the tool ran, whether it succeeded and how long it took. No file data, no identifier, no cookie.
Your file is not on that list. How this works.
Frequently asked questions
Mono files are about half the size and play consistently on single-speaker devices — ideal for voice, podcasts and phone audio.
Mono combines the left and right channels into one, so any stereo separation is lost, but the audio itself stays clear.
Converting mono to stereo copies the single channel to both sides; it won't recreate stereo separation that was never recorded.
Yes — Mono / Stereo is completely free. There's no account, sign-up, watermark or limit.
No. It runs in any modern browser — Chrome, Edge, Safari, Firefox, Brave — with nothing to download or install.
Looking for something else?
- The file is simply too largeCompress Audio
- One side is quieter than the otherAdjust Volume
- You are trying to remove the vocalVocal Remover
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