Mono ↔ Stereo Converter
Stereo to mono, or mono to stereo: pick a direction and get the file back as M4A, Opus, WAV, or FLAC.
Runs entirely in your browser — your files and text never leave your device.
Drag & drop your file here, or
To mono averages all channels into one — handy for voice and smaller files. To stereo duplicates a mono track into two channels so it plays on stereo systems (it won't add real width).
M4A (AAC) and Opus are compact and play everywhere; WAV is uncompressed and FLAC is compressed lossless — both larger, best for editing. MP3 export isn't offered (see the FAQ).
Working on your device — keep this tab open until it finishes.
How to use
- Hand it the audio file. A player appears underneath once the file decodes, which is your chance to hear what you started with.
- Set Channels. To mono is already selected when the page loads, so press To stereo only if you are going the other way.
- Choose an output format. M4A is the default; Opus, WAV and FLAC are the other three.
- Press Convert & download.
- Watch the bar. Cancel sits right beside it if you realise you picked the wrong direction.
- Play the result in the second player, then hit Download. The file arrives as converted plus the extension of the format you chose.
About this tool
Half the recording plays in the left ear and the right one sits silent. Or an upload gets bounced because the platform expects two channels and the file only has one. Both of those are channel-layout problems, and this goes in either direction: stereo to mono, or mono to stereo.
To mono averages every channel into one. A stereo file gets left plus right divided by two; a 5.1 file gets all six divided by six. Averaging rather than adding is why nothing clips, because the peak of the result can never rise above the loudest channel that went in. For speech it is close to a free win, since a voice sits in the middle of the stereo picture anyway and a 16-bit WAV comes out at exactly half the bytes.
To stereo does the mechanical thing and copies the one channel into two identical ones. The file is then stereo by every definition a player cares about, and it sounds precisely as it did before, dead centre. Nothing invents width. Hand it something that already has two channels and To stereo passes the audio through untouched, which leaves you with a format change and nothing else.
Four output formats sit under the toggle. M4A (AAC) and Opus are the small ones. WAV is uncompressed 16-bit and FLAC is lossless compression, both larger, both right when the file is heading back into an editor. Sample rate is left alone from start to finish. If the level is uneven as well, run the Audio Normalizer afterwards, and the Audio Converter covers a plain format change on its own.
A four-minute interview, folded to mono
Say a phone recorded a four-minute interview as a 48 kHz stereo WAV. Two channels, 48,000 samples a second, 240 seconds, 16 bits each: roughly 46 MB. Load it, leave Channels on To mono, and keep the M4A default.
The channel math finishes before you notice it. What the progress bar is actually showing is the AAC encode. The file that lands is converted.m4a, one channel, still 48 kHz, and both ears finally hear the same thing.
Good to know
- Mono to stereo duplicates a channel. The file becomes two-channel and the sound stays exactly where it was, in the middle. There is no spatial information hiding in a mono track to recover.
- Feeding an already-stereo file into To stereo leaves the audio alone. You end up with a format conversion and identical channels.
- Folding a wide mix down averages the channels, so anything panned hard to one side ends up quieter against the middle. Material that is out of phase between left and right can cancel almost to nothing.
- MP3 is missing from the format list. Bundling an MP3 encoder needs a licence this site has never taken on. M4A fills the compact slot instead.
Frequently asked questions
Will going mono fix audio that only plays in one ear?
If the recording genuinely has content on one side and silence on the other, then yes. Averaging the two puts the material in the centre at half its old level, so run it through the Audio Normalizer afterwards to bring the volume back. A faulty cable or earbud is a different problem and no conversion will touch it.
Does mono really halve the file size?
For WAV it is exactly half, because every sample of every channel is stored literally. For M4A, Opus and FLAC the saving is real but smaller, since those encoders already take advantage of how similar two channels usually are.
Where is MP3 in the format list?
Left out on purpose. Bundling an MP3 encoder brings licensing this site would rather avoid, so M4A (AAC) and Opus cover the compact slot instead. M4A plays anywhere an MP3 would, and Opus gets you a smaller file when you know the destination handles it.
Does it change the sample rate or the quality?
Sample rate comes out the same as it went in. Everything is rendered to 16 bits first, then WAV keeps that exactly and FLAC compresses it without loss. M4A and Opus re-encode, which adds one lossy generation on top of whatever the source already had.
What about 5.1 and other multi-channel files?
To mono handles them fine. All six channels of a film soundtrack are averaged into one, not just the front pair. The other direction only ever produces two channels, so there is no 5.1 output here.
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