Turn mono audio into stereo — and know what you are getting
This mono to stereo converter turns a one-channel recording into a two-channel file. The simplest method copies the mono signal to both speakers, which fixes the most common complaint: a voice memo, old recording or single-mic podcast that only plays in the left earbud. For a sense of space, two widening methods spread the sound across the speakers, and a pan control places it exactly where you want it in the stereo field.
An honest note first: true stereo can’t be recreated from mono. A stereo recording captures timing and level differences between two microphones; a mono file contains one mixed signal with no information about where each instrument was. Widening creates a pleasant impression of width, but it cannot move the guitar left and the piano right. The page tells you which method does what, so you can choose with open eyes.
How to use the Mono to Stereo Converter
- Drop one or more mono files on the upload area. Each row shows the format, sample rate, bitrate and channel count.
- Choose a Stereo method: Duplicate, Haas widening, Mono-safe widening or Pan position.
- Adjust the delay and delayed side, the width, or the pan position for the chosen method.
- Keep the original format, or choose WAV, FLAC, MP3, AAC, Opus or Ogg Vorbis and a bitrate.
- Press Make stereo, compare Before and After on headphones, and download the file or a ZIP.
Mono to Stereo Converter features
Bit-exact dual mono
Duplicate copies every sample to both channels unchanged, so a WAV result is a lossless stereo version of the original.
Haas widening
Delays one side by 5–35 ms. Your ears fuse the two copies into one wide sound that leans towards the earlier side.
Mono-safe widening
Adds and subtracts a delayed, high-passed copy, so left plus right equals the original exactly and nothing cancels on a mono speaker.
Constant-power panning
Places the sound anywhere from hard left to hard right with a −3 dB centre, so loudness stays even as you move it.
Keeps format and tags
MP3 in, MP3 out, with title, artist and cover art preserved; or convert to another format at the same time.
Batch and preview
Convert many clips at once and listen to each result before downloading.
Which stereo method should you use?
| Method | What it does | Mono-compatible | Best for |
|---|---|---|---|
| Duplicate | Same signal in both channels | Yes, perfectly | Voice notes, podcasts, video edits, fixing one-ear playback |
| Haas widening | One side delayed by 5–35 ms | Partly — comb filtering when summed | Single instruments, synths, backing vocals |
| Mono-safe widening | Adds ± a delayed, filtered copy | Yes, the sum equals the original | Music beds, ambience, anything that may play on one speaker |
| Pan position | Moves the sound left or right | Yes | Placing a voice or instrument in a stereo mix |
How the widening works
Haas widening uses the precedence effect: when the same sound reaches both ears within roughly 1–35 milliseconds, the brain hears one event coming from the side that arrived first, but it feels broader. Around 10–20 ms sounds wide without an audible echo. The drawback shows up when the two channels are added back together on a phone speaker or a mono Bluetooth box: the delay causes comb filtering, a hollow, phasey colour.
Mono-safe widening builds the stereo pair as left = mono + side and right = mono − side, where “side” is an 11 ms delayed copy with the bass below about 250 Hz removed. When the channels are summed the side signal cancels completely and the original returns untouched, so the file is safe for radio, smart speakers and club systems that play in mono. To make sure it can never clip, the result is scaled by 1 ÷ (1 + width), for example by about 3.5 dB at the default 50% width.
Tips
- Speech and podcasts almost always want plain Duplicate — widening a voice makes it sound distant.
- Check the result on headphones and on a single speaker; if it sounds hollow in mono, switch to mono-safe widening.
- Converting an already-stereo file? It is mixed to mono first. To change an existing stereo image instead, use the Audio Channel Converter.
- Going the other way, for smaller voice files, the Stereo to Mono Converter mixes stereo down safely.
- The effects are computed in the page itself; Mediabunny (MPL-2.0) handles decoding, and LAME and libavcodec (LGPL), libFLAC and libvorbis (BSD) encode the formats that need them.
Mono to Stereo Converter FAQ
How do I convert mono to stereo?
Drop the file on this mono to stereo converter, keep “Duplicate (dual mono)” selected and press Make stereo. The result has the same sound in both channels, so it plays in both ears and both speakers.
Can you make real stereo from a mono recording?
No tool can. Real stereo needs the direction information captured by two microphones or a stereo mix, and a mono file doesn’t contain it. Widening only creates an impression of width.
Why does my mono file only play in one ear?
Some players send a one-channel file only to the left output, and some recorders save a “stereo” file with silence on one side. Converting to dual mono puts the sound in both channels.
What is the Haas effect?
It is the precedence effect: a sound repeated within about 35 ms is heard as a single sound from the direction of the first arrival. A small delay on one channel therefore makes a mono sound feel wider.
Will the stereo file be twice as big?
For WAV and FLAC, roughly yes, because there are two channels of samples. For MP3, AAC, Opus and Vorbis the size follows the bitrate, which you can keep the same.
Is it free and private?
Yes. There is no limit or watermark, and the audio is processed only in your browser.