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Video & Audio Tools

Mono to Stereo Converter

Give mono recordings two channels. Copy the sound to both sides for compatibility with players, editors and platforms that require stereo; place it anywhere between left and right with constant-power panning; or widen it with a subtle delay between the channels for a sense of space. Stereo files with mono content are handled too.

  • Files stay on your device
  • No sign-up
  • Free to use

How to use Mono to Stereo

  1. Drop a mono audio file onto the page.
  2. Choose duplicate, pan or widen.
  3. Adjust the position or width.
  4. Convert and download.

Mono to Stereo features

Duplicate

Identical channels, centred sound.

Pan

Constant-power placement left to right.

Widen

Haas-effect pseudo-stereo.

Level kept

No loudness jump when panning.

Any format

MP3, M4A, WAV, FLAC.

Private

Processed in your browser; nothing is uploaded.

When to use Mono to Stereo

  • Meeting stereo requirements of platforms and editors.
  • Placing voices left and right in a dialogue.
  • Adding space to mono instrument recordings.
  • Fixing mono audio that plays on one side only.

Mono to Stereo FAQ

Is this real stereo?

No conversion can create true stereo from one channel. Duplicating keeps the sound centred; widening adds an illusion of width.

What is the Haas effect?

When the same sound reaches one ear a few milliseconds later, we perceive it as wider rather than as an echo. Delays of 10–20 ms work well.

Will widened audio sound bad in mono?

Played back in mono, the two delayed copies can colour the sound slightly. Use duplicate mode if your audience listens on mono speakers.

Why constant-power panning?

It keeps the perceived loudness the same at every position.

Why does the first run take longer?

Re-encoding uses FFmpeg compiled to WebAssembly (about 32 MB), which is downloaded once and then cached.

Which formats can I use?

MP3, WAV, M4A/AAC, OGG, Opus, FLAC, WMA and AIFF, and the audio of MP4, MOV, WebM and MKV videos. Save in the original format or as MP3, M4A, WAV or FLAC.

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From one channel to two

Mono recordings are common: voice memos, many microphones, old recordings, phone calls. Some tools and platforms expect stereo files, and some mono files play from only the left speaker because they were saved incorrectly. Converting to proper stereo solves both problems.

Duplicate mode copies the single channel to left and right. The listener hears the sound in the centre, exactly as intended, and every stereo player handles the file correctly. For a stereo file that contains mono content, the two channels are averaged first.

Pan mode places the sound in the stereo field using constant-power panning: the levels follow a quarter sine and cosine curve, so the sound does not get louder in the centre or quieter at the sides. This is how mixing consoles position mono sources.

Widen mode uses the Haas effect, adding a short delay to the right channel. The brain interprets the difference as width. It is a simple, effective trick for instruments and ambience, though not for voices that must stay centred.

The conversion runs in your browser.

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