Is this the same as inverting the phase by 180 degrees?

In the way the phrase is used by mixing consoles and plugin interfaces, yes: the polarity button and the 180 degree label describe the same operation. Technically it is polarity inversion rather than a true phase shift, since every frequency is mirrored in sign rather than delayed by a fixed time.

What is a null test and why would I run one?

It is a comparison. Invert one copy of a signal, sum it with the other at matched level, and everything the two have in common cancels. Whatever is left is their difference, which is how you hear a reverb tail, a noise floor or any processing that two takes do not share. The panel suggests summing the original with the inverted copy for exactly this.

When should I invert a whole file rather than one channel?

When the entire source is out of polarity with something else. A reversed DI, a wrongly wired split or an interface that flips polarity can all invert everything at once, and in that case a whole file flip restores the relationship. If only one side of a stereo pair is wrong, inverting both would make the problem worse.

My null test is not perfectly silent. Did something go wrong?

Not necessarily. A null only cancels the parts that are identical, so any difference in level, timing, filtering or processing leaves residue, and that residue is the answer you were looking for. A slightly incomplete null is normal; a wildly incomplete one usually means the two files are not the same take.

Does inverting polarity change the sound?

In isolation, no. Listen to a single track flipped in polarity and it sounds exactly the same, because the ear does not detect absolute polarity reliably. The audible effect only appears in relation to other signals, which is why the operation matters during mixing and cancelling rather than on its own.

Phase Inverter

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Channel Inverter

Invert audio channel polarity

DC Offset Remover

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Phase Meter

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Correlation Meter

Measure stereo correlation

Phase Inverter multiplies the entire signal by minus one, which is what mixers and plugin interfaces mean by the polarity button. Every sample's sign flips, on every channel at once.

What is Phase Inverter?

Drop a file and download the inverted copy. The footer spells out the two uses directly: fixing polarity cancelling overlaps in multi microphone recordings, and null testing two takes to hear only what they do not share.

What the operation is:

An exact negation of every sample across every channel, with no scaling and no smoothing.
One operation rather than per channel choices, so the internal relationships in the file are preserved.
A null test described in the panel: sum the original and the inverted copy at matched level, and whatever survives is the difference.
An output WAV named after the source with a phase flip suffix.

Inverting polarity is multiplication by minus one, applied to the waveform sample by sample. It is not a delay, and it is not the frequency dependent phase rotation a filter introduces; it is a mirror image about the horizontal axis, which means two copies of the same signal that meet with opposite polarity cancel almost completely when summed. That property is what makes the operation useful in two opposite directions. Used on one of a pair of misaligned sources, it restores reinforcement where a reversed cable, a wrongly pinned splitter or a reversed DI had been causing cancellation during tracking. Used on a copy of the same take, it turns the pair into a difference signal, so a null test of 180 degrees reveals reverb tails, noise and every element the two takes do not share. Verified behaviour is that the negation is exact, so applying it twice returns the original samples.

What it cannot do:

It flips polarity rather than aligning time, so a source that is late by even a fraction of a millisecond needs a delay instead.
A null test only cancels the parts that are identical, so residual level is expected rather than a sign that something failed.
Inverting a single channel of a mix can cancel centre content, which is destructive when that was not the intent.
The tool offers no per channel choice, so a polarity problem in one channel only has to be handled with the channel inverter.
It cannot detect or report cancellation, so the mono sum test still has to be performed elsewhere.
A partial null often points to level, timing or filtering differences that no polarity flip will resolve.

Reach for it when a mono fold down loses level and you have established that polarity is the cause, and use it again in reverse when two supposedly identical takes need to be compared. Treat it as a comparison tool as much as a repair: a null test is one of the few ways to hear what a processing chain actually did to a signal, because anything the chain added or changed survives the cancellation while the original content disappears. If only one channel is misbehaving, the channel inverter gives you the same exact negation with a per side choice, and the swapper is the tool for channels that sit in the wrong places rather than the wrong polarity.

How to use Phase Inverter

Drop an audio file onto the panel; the whole signal will be inverted regardless of how many channels it has.
Run the pass, which negates every sample of every channel exactly.
Download the inverted WAV, named after the source with a phase flip suffix.
Sum it against the original at matched level elsewhere if you want a null test to reveal the difference.

When to use Phase Inverter vs related tools

Phase Inverter is the whole file polarity flip, so it suits repairing a reversed source and setting up a null test between two takes. Channel Inverter does the same negation with a per side choice, which is what you need when only one channel of a pair is out of polarity. When the underlying issue is the position of the channels rather than their sign, Left/Right Channel Swapper exchanges them, and DC Offset Remover fixes the related problem of a waveform that sits off centre.

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