The Ø button in the RØDECaster Pro II's microphone channel is known as a Phase switch/button.
The phase button, often labelled as a "Phase Invert" or "Polarity Reverse" is a function that allows you to reverse the phase of an audio signal by 180 degrees. This means that it flips the waveform of the signal upside down. When engaged, the phase button swaps the positive and negative halves of the waveform.
The primary purpose of the phase button is to address phase-related issues in audio signals, especially when working with multiple microphones or audio sources.
When two or more microphones capture the same sound source such as a piano, snare drum and a guitar, their signals may be out of phase with each other due to differences in distance or microphone placement. This can lead to phase cancellation, where certain frequencies are attenuated or even completely cancel out an audio signal or make the audio sound tinny or flat when monitored.
Engaging the phase button on one of the channels can help align the phases and reduce or eliminate cancellation issues.