Two waves are often referred to as being ‘out of phase’ if their peaks and troughs aren’t perfectly aligned, but the most important implication from a production perspective occurs when the waves are 180º out of phase, meaning their amplitudes are identical in magnitude but one is positive and one is negative.
Take the example of two waveforms which are identical in terms of frequency/wavelength but 180º out of phase with each other. At any given moment, their amplitudes will add up to zero – and the result will be silence. Likewise, the sum of two identical signals which are out of phase by 90º or 270º will be lower than the sum of two in-phase waves, weakening the combined amplitude.
