Mono to stereo converter — stereo WAV from a mono file

What does mono to stereo mean here?

A mono file has one channel. A stereo file has two: left and right. This converter decodes a mono file in the browser and writes a 16-bit stereo WAV where both channels carry that same signal. The sound stays centered. It does not recover a stereo recording that was never captured. If the file is already stereo, the page says so and does not pretend to convert it.

What the converter does

A local mono check, an optional widening delay, and a stereo WAV download.

1. One channel copied to left and right: A true mono file becomes a two-channel WAV. With the delay at 0 ms, the samples on both sides match, which is the honest dual-mono result.
2. Optional right-channel delay: A delay from 1 to 20 ms shifts only the right channel. That is a widening effect. It is not the original stereo image of a performance.
3. Already-stereo files are left alone: If the decoded file has two channels that differ, the page reports stereo and does not offer a download. If the two channels already match, it reports dual-mono.
4. 16-bit PCM WAV: The download is a standard stereo WAV: 16-bit integer samples, two channels, at the sample rate the browser decoded. Other containers are not written.
5. Decoded in the browser: The file is not uploaded. Decoding uses the Web Audio API, then the WAV is built on this device. Files over 40 MB or longer than 8 minutes are refused.

How to convert mono to stereo

Use a file that really has one channel. WAV and MP3 are the most reliable inputs.

1. 1. Choose the audio file: The page decodes it locally and reports the channel count, sample rate, and duration. A file the browser cannot decode shows an error instead of a download.
2. 2. Leave the delay at 0 unless you want an effect: 0 ms copies the mono channel to both sides. Raise the delay only if you want the right side slightly late. The label on the control calls that an effect.
3. 3. Download the stereo WAV: The file name ends in -stereo.wav. Open it in any editor that reads WAV and confirm the channel count is 2.

Know what the stereo file contains

Two channels are not the same thing as a stereo recording.

1. Centered audio is the expected result: Identical left and right samples play from the middle. That is what a mono source should do in a stereo file. Headphones will not suddenly place sounds on one side.
2. Do not run a stereo mix through this tool: Collapsing a real stereo file to mono and back would throw away the width. This page refuses files whose channels already differ.
3. A short delay is not recovered ambience: The right channel is a copy, shifted by a few milliseconds. Room sound, panning, and a second microphone are not in the file, so they cannot be restored.
4. Keep the clip under the limits: The page stops at 40 MB and 8 minutes of decoded audio so the WAV can be built in memory without stalling the tab.

Sources & References

References for stereo sound and for decoding the file in the browser.

• Stereophonic sound

  “Stereophonic sound, commonly shortened to stereo, is a method of sound reproduction that recreates a multi-directional, three-dimensional audible perspective. This is usually achieved by using two independent audio channels through a configuration of two loudspeakers (or stereo headphones) in such a way as to create the impression of sound heard from various directions, as in natural hearing.”

  This converter creates the two-channel container. With the delay at 0 ms the channels are not independent, so the image stays centered. en.wikipedia.org/wiki/Stereophonic_sound

• decodeAudioData

  “The decodeAudioData() method of the BaseAudioContext Interface is used to asynchronously decode audio file data contained in an ArrayBuffer that is loaded from fetch(), XMLHttpRequest, or FileReader. The decoded AudioBuffer is resampled to the AudioContext's sampling rate, then passed to a callback or promise.”

  The chosen file is decoded with that method. Channel data is copied out, then written into a 16-bit stereo WAV on this device. developer.mozilla.org/en-US/docs/Web/API/BaseAudioContext/decodeAudioData

Frequently Asked Questions

Have questions? We have answers.

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