[Kiwiburger]

Phase and polarity are two different issues, and it helps to understand why you might want to do something like this.

Phases is all about the timing of things that progress in a cycle - like phases of the moon. Since audio is about waveforms in air, when you have multiple sources of waves from the same sound source being mixed - there is the potential for the waves to either combine constructively, or destructively. If two identical signals combine with a 0 degrees phase difference, the sound gets 6dB louder. If they combine with a 180 degrees difference, you get complete nulling cancellation.

The phase difference is caused by the time delay between the two signals. But phase difference is not quite so simple as time delay. Because sound is not just a single fixed sine wave - it's a complex mixture of waves of every possible shape and frequency. So a fixed time delay (such as the speed of sound time difference between two microphones) is going to cause different phase shifts for each different frequency ... have a think about that for a moment ...

Obviously when there are two microphones on the same sound source, there is a whole range of phase shift problems - depending on frequencies. Some frequencies will be in phase, and get the 6dB boost. Some will cancel, and be totally nulled. And everything in between ...

So suddenly - a simple two position 'phase' switch is starting to look a little inadequate ...

Technically - it's not really a phase switch - it's a polarity switch. The reason it's called a phase switch is because a balanced signal, such as a microphone, has two 'phases' - actually polarities - due to the two wires being alternatively negative and positive.

Polarity is polarity - it's about the direction the mic diapragm goes - forward or backwards. It's about the direction the electrons flow - negative or positive. It's about the direction the speaker goes - forward or backwards.

When you hit a snare drum - the stick pushes the skin downwards, creating a low pressure zone of air above it. A mic diapragm above the snare will be forced downwards, following the acoustive waveform in the air. This generates a voltage ... etc, etc, and ultimately we want our speaker cone to travel backwards - so when we listen we get the same effect of air initially rushing away from us.

If the polarity of any of our wires were reversed at any point - we would get the opposite effect - the speaker cone would jump towards us. A very subtle, and probably insignificant difference. But it becomes significant when we have two mics on the same drum. We really want the two waveforms to reinforce each other, not cancel each other out.

In real life - the difference between the top and bottom mics will be a very complex relationship of polarity, time and phase differences. It makes sense to flip the polarity switch on one of the mics, because the mics are facing 180 degrees apart. But because of the time and phase differences, it's still possible for the combination of the two mics to sound bad. So really, you have the choice of flipping the switch for a choice of two options. Or you can move the mics.

PS - the real reason why preamps and mixers have polarity switches? In the early days, the Brits and the Americans had different wiring standards for balanced connectors. It's only recently that the standard Pin 2 Hot has become the standard. Before then, different equipment had different wiring. So instead of having to rewire your cables, you could just flip a switch.

Cubase has a phase switch in your mixer channels.