How it works
- Drop your audio file. MP3, WAV, FLAC, AIFF, OGG or M4A up to 500 MB — it's decoded locally, nothing is uploaded.
- Choose the channels and invert. All channels (the usual case), left only or right only for stereo troubleshooting.
- A/B and download. Switch between the original and the inverted version on the waveform, then export in the same format as your source.
Features
- Three inversion modes. Invert every channel, the left channel only, or the right channel only.
- A/B preview. Compare the original and the inverted version on the waveform before downloading — switching is free.
- Measured null test. The original and the inverted file are summed sample by sample: the residual is shown in dB below the signal (perfect silence for lossless files), and a stereo file gets a left/right correlation check that flags a channel with inverted polarity.
- Align two tracks (option). Drop a reference and a second recording of the same source (two mics, DI + amp, two bounces): the tool finds the delay, to the sample and up to ±500 ms, and the polarity, exports the second file aligned in its own format, and measures the null test before and after. On very repetitive sound it says the delay is uncertain instead of guessing.
- Same-format export. Lossless sources stay lossless (WAV, AIFF, FLAC); lossy sources are re-encoded at high quality.
- 100% in your browser. Your track never leaves your computer — processing runs locally with ffmpeg.wasm.
FAQ
Is this phase invert tool free?
Yes. Without an account you get 2 free uses per day across AudioKit's free tools; with a free account, 5 per day. A use is only counted when you download a result; loading files, measuring and A/B-ing are free, and downloading the same result again is free too. AudioKit Premium removes the daily limit.
Is my audio file uploaded to a server?
No. The file is decoded, inverted and re-encoded entirely in your browser with ffmpeg.wasm and never leaves your machine. The only network call is a tiny anonymous counter that tracks your daily free quota.
Which audio formats are supported?
MP3, WAV, FLAC, AIFF, OGG and M4A files up to 500 MB. The inverted file is exported in the same format as the source: lossless stays lossless, lossy formats are re-encoded at high quality. With a lossy file (MP3, OGG, M4A) the null test is never perfectly silent: the re-encode leaves a small codec residual, which the tool measures and shows in dB.
What is polarity (phase) inversion used for?
Three classic jobs. Fixing phase problems: when two takes of the same source (top/bottom snare mics, a flipped cable, a DI plus a mic) cancel each other, flipping one of them restores the punch. Null tests: play an inverted file against the original — perfect silence proves the two are identical. And cancelling a signal: subtract a known part from a mix by summing it inverted.
Can it align two tracks (two mics, DI and amp)?
Yes, with the “Two files: align” option. Drop the reference (A) and the track to align (B): the delay of B (to the sample, up to ±500 ms) and its polarity are measured by cross-correlation over the whole file, then B is exported shifted and flipped if needed, same length and format, while A stays untouched. The null test A − B is measured on the file you download, before and after. Two different mics never cancel completely: what remains is their real difference. With very different tones, the best-sum setting can differ from the physical distance between the mics, so check by ear. On very repetitive sound (sustained note, loop, pure tone) several delays fit equally well: the tool says it is uncertain and exports nothing.
Why does the inverted file sound exactly the same on its own?
Because that's the physics: inverting polarity just turns the waveform upside down, and your ears don't perceive absolute polarity on a single signal. The flip only becomes audible when the file is summed with another signal — against the original it produces silence, against a phase-shifted twin it changes the tone. So judge it in context (your DAW), not solo.