Mono to stereo. Honest dual-mono, no fake widening.
For tools that demand a stereo file but you only have a mono recording. We duplicate the mono channel into both L and R — sounds identical, satisfies the format requirement. No artificial widening, no chorus tricks, no phase weirdness when someone plays it back through a mono speaker.
drop your mono audio
WAV, MP3, M4A, OPUS — any mono file. Batch supported. Stereo files pass through unchanged.
When you actually need this
- Podcast platforms that require stereo — some intake systems reject mono outright even though stereo voice content is wasteful. Dual-mono fixes it.
- Video editors that want stereo audio — some old or simple editors silently mute mono tracks. Duplicating to stereo restores playback.
- Hardware samplers needing stereo input — certain pads/slots only load stereo files.
- Streaming intake (Spotify, Apple Music, distributors) — they prefer stereo masters. If your master is mono (uncommon but happens for spoken word), dual-mono is the right delivery.
- Mixing in a DAW where every other track is stereo — keeping consistent channel count avoids weird pan-law artifacts.
- Karaoke-style backing tracks — some karaoke players demand stereo files even for instrumental-only mono masters.
What we don't do
We don't apply fake stereo widening — no Haas delay, no Lexicon "stereoize," no chorus pseudo-stereo, no comb filtering. Those tricks sound wide on headphones but cause comb-filter colorations or outright cancellation when summed back to mono (which happens often: laptop speakers, phones, mono PA systems, Bluetooth speakers).
If you want real spatial width, do it in a DAW with informed choices about reverb, delay, and stereo placement. This page is for the case where you just need a stereo container.
What about going the other way?
For stereo → mono, see our dedicated stereo-to-mono page. That's the more common direction (cut file size for voice, transcription, podcasts).
FAQ
Will the sound be different in stereo?
No. Identical content in both channels = centered mono image, just like the original. Difference: the file has two-channel headers and is roughly 2× larger as WAV.
Why does my mono MP3 already show as stereo?
Some encoders write a stereo header even when both channels are identical (joint stereo). The decoded audio is still effectively mono. Check the actual channel content (in Audacity's "Track Info") to be sure.
Can I do this batch-style for a folder?
Yes. Drop multiple mono files, get a zip of dual-mono stereo files back.
What if I drop a stereo file by mistake?
We'll detect it and pass it through unchanged. Stereo stays stereo.
Does my audio get uploaded?
No. Everything runs in your browser tab.
What happened to my mono mid/side info?
Mono has no mid/side — there's just one channel. Both stereo channels become that one. If you want to fake "side" content for width, you'd need to add reverb/delay, which we deliberately don't do.
Why would I convert mono to stereo?
Some upload tools, video editors, and platforms refuse mono input. Duplicating mono into a two-channel WAV or MP3 (L=R, identical audio in both channels) satisfies the format requirement without changing how the audio sounds — both ears still hear the same thing.
Will this make my mono recording sound stereo?
No. The file has two channels but identical content in each — the listener still hears it as centered mono, just packaged as a stereo file. There's no fake widening, chorus, or pseudo-stereo effects applied. Honest dual-mono only.
Why don't you apply fake stereo widening?
Fake stereo (Haas delay, comb filters, chorus tricks) often sounds gimmicky and creates phase problems when summed back to mono — common on phones and laptop speakers. If you want spatial width, record in stereo or process with proper plugins in a DAW. We won't pretend to make mono into something it isn't.
What file size impact does mono→stereo have?
WAV doubles in size (two channels of PCM instead of one). MP3 grows slightly less because the encoder detects the channels are identical and uses joint stereo (mid/side) coding efficiently — typically 15-30% larger, not double.
What's the use case for this?
Uploaders that reject mono (some podcast platforms, some video editors, some streaming intake systems), DAW projects where everything else is stereo and you want consistent channel count, certain hardware samplers that only accept stereo files.
Does anything upload?
No. Conversion is in-browser.