Phase

‘Phase’ is the position in time of a waveform cycle.

It is measured in degrees and is an important factor in recording and mixing due to the effect of phase cancellation of sound waves. When a frequency overlaps another and is  180 degrees out of phase, both waves will cancel completely.

In recorded music, phase is often an issue when mixing multiple microphone sources, as if they are not correctly placed they can cause phase cancellation, phase amplification, or phase shifting.

In film sound, phase comes in to play when using stereo effects, folding stereo down to mono, and when mixing in stereo or 5.1.

image of 2 waveforms offset in phase
This represents two waveforms, whose phase is offset by about 45 degrees, causing phase shifting.
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