Lots of people, myself included, silently correct anyone who refers to “flipping the phase”, “pressing the phase button” or similar. If that is you then you are also a pedant and welcome to my world. As well as being a pedant I also understand that many of the people saying it “wrong” understand the difference between polarity and phase and are using it in the vernacular. It’s fine to use it that way as long as you are aware of the difference. But what if you don’t? What harm does it do to use “phase” wrong?
The issue is that polarity is simple to understand, it’s very tidy and gives predictable results. Phase isn’t discussed as often, is harder to understand and people might conclude that because they understand polarity, they understand phase – no they don’t.
Polarity inversion is the reversal of the positive and negative voltages in an electrical signal. If you swap the positive and negative connections then the voltages will be reversed and everything which was on the positive side of zero volts becomes negative and vice versa. The waveform is turned upside down to become the exact opposite of its un-inverted form. This is incredibly useful for all sorts of reasons.
Phase describes the relationship between two periodic alternating signals, it’s related to delay but it’s not quite the same. It describes the offset between the two waveforms in terms of how far through its cycle from positive to negative and back again it is. Crucially this is frequency dependent so as frequencies vary, so do phase relationships. Phase is measured in degrees with a whole waveform cycle being made up of 360 degrees. This offers a way to talk about these relationships without reference to frequency, delay or anything else.
It is easiest to understand these relationships when talking about multiple versions of the same signal but phase relationships can affect signals which differ, things just get messier the more different the signals are so for clarity examples tend to involve identical sine waves. If you delay one signal against the other you affect their mutual phase relationship. If you delay identical signals by exactly half a waveform then a 180 degree phase relationship exists between them and they will cancel when summed together. This is the same outcome as inverting the polarity but the 180 degree phase relationship has been caused by a different mechanism – Changing the time relationship between the two signals rather than the voltage relationship.
Neither changing the time or voltage relationship manipulates the phase directly. This can be achieved using phase rotators. If you’ve ever wondered what an all pass filter does, it rotates the phase of a signal. Phase rotation goes beyond the scope of this article but I cover it in some detail in this video about Sound Radix Pi, which is a dynamic phase rotator.