Phase describes where a periodic waveform is in its cycle at a given time. The relationship in time between two or more waveforms with identical or harmonically related periods gives us a measurement of their phase difference.
Phase relationships are extremely important during all stages of audio production, as out-of-phase waveforms, whether they spring up during recording or throughout the later stages of production, will wreak absolute havoc on your mixes. These out-of-phase waveforms result in an unpleasant phenomenon that’s known as phase cancellation.
In this post, we’ll do a deep dive into phase cancellation, what causes it, how you can identify it, and — ultimately — what you can do about it.
Phase vs. Polarity — There’s a difference
Before we dive into phase and phase cancellation, we should first discuss the concept of polarity, as it’s very easy to confuse the two. In a nutshell, phase is a function of time, while polarity is a function of positive and negative changes.
Polarity really comes into play during the recording process, as you’ll want to ensure that your loudspeaker moves in the same direction as the microphone membrane while it captures a sound source. During the initial attack of a sound, your mic creates a positive voltage, passes it through a cable and preamp and into your recording device, then finally out of a speaker.
If you’ve maintained correct polarity throughout your entire signal chain, your speaker will move in a positive direction with every initial attack of your sound source. If you haven’t maintained correct polarity, your signal will do the opposite, which can cause destructive interference when combined with other signals with correct polarity.
Signals can be anywhere from zero to 180 degrees out of polarity, with zero being in correct polarity and 180 being in reverse polarity, which will result in complete signal cancellation.
While you may not notice incorrect polarity with a single sound source, it will most certainly cause issues in a multitrack recording.
The easiest way to understand polarity is to run identical signals through two speakers. Then, flip the polarity of one of the speakers 180 degrees by reversing its positive and negative wires.
Doing this will cause the two signals to cancel each other out.
When a microphone is 180 degrees out of polarity, you’ll get a similar result to that of reversing the polarity on a loudspeaker. That’s why most mixing consoles, DAWs, and mic preamps include a polarity reverse function.
To reiterate: polarity is a function of positive and negative changes and phase is a function of time relationships. While these two terms are sometimes used interchangeably, they are not the same thing and must be addressed separately. ….
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