What are the pros and cons of using phase invert switches on your mic preamps or mixers?

1 What is phase and polarity?

Phase is the relationship between two or more signals that have the same frequency and wavelength, but differ in their starting point or position. When two signals are in phase, they add up constructively, creating a louder and fuller sound. When they are out of phase, they cancel each other out, creating a quieter and thinner sound. Polarity is the direction of the electrical current or voltage of a signal. When two signals have the same polarity, they are positive or negative at the same time. When they have opposite polarity, they are positive and negative at different times. Flipping the polarity of one signal is equivalent to shifting its phase by 180 degrees.

3 How to use phase invert switches?

Phase invert switches are usually located on your mic preamps or mixers, either as a button or a switch. They are often labeled as "phase", "polarity", or "?". To use them, you need to listen to the signals that you want to compare, and flip the switch on one of them. Then, listen to the difference, and decide which option sounds better. You may need to adjust the volume or pan of the signals as well. You can also use your ears and a pair of headphones to check for phase issues before recording. Simply move one mic closer or farther away from the sound source, and listen to how the sound changes. If you hear a loss of low frequencies, or a thinning of the sound, you have a phase problem. You can either move the mic again, or use the phase invert switch to fix it.

4 What are the drawbacks of using phase invert switches?

Phase invert switches are not a magic bullet that can solve all your phase problems. Sometimes, flipping the polarity of one signal may not be enough, or may even make things worse. This is because phase is not only affected by polarity, but also by time and distance. If two mics are placed at different distances from the sound source, they will capture the sound at different times, creating a phase difference that cannot be corrected by polarity alone. You may need to adjust the mic placement, or use a delay or a phase alignment plugin to align the signals more precisely. Also, phase invert switches may introduce unwanted artifacts or noise into your signal, especially if you use them on digital devices or converters. You may need to check for clicks, pops, or distortion, and use a noise gate or a filter to remove them.

5 What are the alternatives to using phase invert switches?

Phase invert switches are not the only way to deal with phase issues in your studio recordings. Sometimes, you may want to embrace the phase differences between your signals, and use them creatively. For example, you can use phase cancellation to create a notch filter effect, by placing two mics close together and flipping the polarity of one of them. This can create a frequency cut that can be used to shape your tone or remove unwanted sounds. You can also use phase differences to create a flanger or a chorus effect, by slightly detuning or modulating one signal and mixing it with the other. This can create a sweeping or shimmering sound that can add movement or texture to your mix.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?