Metric Halo SpectraFoo - Manual (Page 118)

Glossary
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Figure 186: 0° Phase offset
The two signals are drawn perfectly on top of each other. In the next example,
the right signal is 180° out of phase with the left signal. When the audio on
the left is at its highest, the right is at its lowest and vice versa. A signal that
is 180° out of phase is also called “polarity inverted” or “phase inverted”
Figure 187: 180° Phase offset
If we sum the signals together, we get nothing; the high of the left is cancelled
out by the low of the right. This is called phase cancellation