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.