Separate the left and right channels of any recording into their own files, pull out the mid (centre) and side (stereo) signals, or fix a stereo file by swapping, inverting or muting one channel. Each file is analysed first so you can see which side carries what.
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Operation
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How to use the Stereo Channel Splitter
Add your stereo files by dropping them on the box or clicking it. Each file shows the level of both sides and their correlation.
Choose an operation: Split left / right, Extract mid / side, or Swap, invert, mute.
Set the options, for example dual mono output, which mid/side files you want, or which channel to invert.
Pick WAV or MP3 and press the green button. All files in the list are processed.
Download each output with its own button (Left, Right, Mid, Side…) or get everything as a ZIP.
Common jobs and the right setting
You have…
Operation
You get
An interview or podcast with one microphone per channel
Split left / right
One clean file per speaker for separate editing and levelling
A camera file with a lavalier on one input and the camera mic on the other
Stereo file with mid on the left and side on the right
A file whose sides are reversed
Swap, invert, mute → Swap
Corrected stereo file
A recording that disappears in mono (negative correlation)
Swap, invert, mute → Invert right polarity
Phase-corrected stereo file
A noisy or broken channel
Swap, invert, mute → Mute left or right
Stereo file with one side silent
The formulas
For each sample, M = (L + R) ÷ 2 and S = (L − R) ÷ 2. Decoding works the other way round: L = M + S and R = M − S. Inverting polarity multiplies a channel by −1, which is not the same as a time delay: it flips every waveform upside down at all frequencies.
The correlation shown for each file is r = Σ(L·R) ÷ √(ΣL² · ΣR²). +1 means identical channels (dual mono), values around 0 mean unrelated channels (for example two separate microphones), and negative values point to a polarity problem. The side level is the energy of S relative to M in decibels; −20 dB or lower means a narrow, nearly mono mix.
File naming
Outputs keep the original name and add a suffix: -left, -right, -mid, -side, -ms, -swapped or -edited. Multichannel files use -center, -lfe, -surround-left and -surround-right, or -ch1, -ch2… for unusual layouts.
Frequently asked questions
How do I split a stereo file into left and right?
Add the file, keep the Split left / right operation and press Split channels. You get two files named after the original with -left and -right added. By default each is a 1-channel mono file; tick dual mono if the file should play on both speakers.
What are mid and side?
Mid is the sum of both channels divided by two, M = (L + R) ÷ 2, and contains everything panned to the centre, such as lead vocals, bass and kick drum. Side is the difference, S = (L − R) ÷ 2, and contains only what differs between the channels, such as reverb, wide guitars and room sound. L = M + S and R = M − S, so nothing is lost.
Can extracting the side channel remove vocals?
Often partly. A lead vocal mixed exactly in the centre is identical in both channels and cancels in the side signal, so the side file is a rough instrumental without the centre. Bass and drums in the centre disappear too, and centred reverb tails may remain.
When should I invert the polarity of one channel?
When a stereo recording sounds thin or hollow, or almost vanishes when played in mono, one channel was probably recorded or wired with reversed polarity. The analysis then shows a negative correlation. Inverting that channel (multiplying it by −1) restores normal stereo.
Does splitting reduce quality?
No. With WAV output the samples of each channel are copied unchanged at the original sample rate (at 24-bit or 32-bit float there is no rounding at all). MP3 output is lossy, as with any MP3 file.
What happens with 5.1 surround files?
In Split mode every channel is saved separately, named left, right, center, lfe, surround-left and surround-right in the standard WAV channel order. Mid/side and the channel tools work on the first two channels (front left and right).
Are my files uploaded?
No. Decoding, splitting and encoding run entirely in your browser with the Web Audio API and a JavaScript MP3 encoder, so your audio never leaves your device.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.