This is a simple technique for comparing two or more different microphones placed approximately at the same position.
Solo both channels and invert the phase of the second channel, then adjust its volume until the sound you’re hearing is the quietest. Essentialy we’re trying to phase cancel the microphones so what you’re hearing is only the subtle differences between the two.
Once you’ve done that, invert the phase of the second channel once again and now you’re left with two level matched signals.