Phase inversion in audio: why channels cancel each other and how to find it
Opposite phase is when two channels recorded the same sound but one of them is flipped. On their own the channels sound fine; mixed to mono they cancel each other and the sound disappears. You cannot hear it in headphones on set. MultiSyncer Studio checks every file after the copy and tells you which channels are in opposite phase.
What opposite phase is
Sound is vibration. If two channels recorded the same sound but one of them is “flipped” (where the first waveform goes up, the second goes down), the channels are in opposite phase, also called reversed polarity. Each one sounds fine on its own. But add them together, for example when mixing down to mono, and they cancel each other: the sound gets thin, hollow or almost disappears.
| Where it comes from | What happens |
|---|---|
| A miswired cable or adapter | One microphone is recorded with reversed polarity |
| A stereo recording from a camera or recorder | Each channel is fine on its own, but in mono the sound vanishes |
Why it is hard to notice
- In headphones on set both channels are heard separately and everything sounds normal.
- The problem shows up later, when the sound is mixed to mono: in the edit, on a phone, on social media.
- To find it by hand you have to listen to every file in mono or check whether the channel waveforms mirror each other. On a day with dozens of files there is no time for that.
How MultiSyncer finds phase inversion
Turn on the sound check
In the project setup, “Footage” section. To check the camera sound too, not only the recorders, set “Camera sound” to “Check”.
Copy the cards
After the copy the app listens to every file. If two channels are in opposite phase, an issue appears: “Channels 1 and 2 in opposite phase” (with the channel numbers).
Listen and decide
The issue applies to the whole file and is shown in “Footage”. Listen to the file and mark it “Fail” or “OK”. Sometimes the opposite phase is intended, then it is “OK”.
Pass it to the editor
A fail reaches the editing app as a red marker, an undecided issue as a yellow one, and the issue goes into the day report. The sound mixer learns about the problem while still on set and can rewire the cable before the next takes.
Opposite phase does not get in the way of sync
For sync, MultiSyncer takes the sound from every channel and track of the camera, and channels in opposite phase do not cancel each other. The clip lands in place even if its channels are in opposite phase.
Markers in the sequence