Phasing

Phasing is a steady or variable cancellation of frequencies created when two copies of identical program material are combined with very small variations in timing. The timing variations that cause phasing are up to approximately 1/2 a video frame apart. When the timing variation between the audio is consistent, the frequencies being cancelled are also consistent, and the result is a steady state, hollow sounding track. When the timing between the audio copies fluctuates, as happens when the same material is combined from two different mechanical transfers, the cancelled frequencies also fluctuate and result in a swishing, variable, hollow sounding artifact.

One common occurrence of phasing in a soundtrack occurs in foreign language re-dubs. Original production effects are edited into a fully filled M&E, and then can be put into the track a second time during the dubbing process. When the two versions of the coincident effects are combined, even with the tightest tolerances for synchronization, there will be small variables in the timing of the signals that result in phasing.

The term flanging is sometimes used interchangeably with phasing, although flanging is generally referred to coincident audio playing back 1/2 to approximately 2 video frames apart.

This audio clip has no phasing.

This is the same audio clip recorded over itself slightly out of phase, thus causing phasing.