MAAT released 2BC multiCORR, a plugin that combines 31 bands of correlation with the monitor controls derived from the free 2BusControl. Details: 31 bands of correlation with carefully chosen center frequencies.
Why the heck do you need a multiband correlation meter? It’s simply that a regular stereo correlation meter doesn´t always show you trouble spots. If your fat kick and bass is mono, it’s mostly correlated so a stereo correlation meter would show that everything is O.K. while your strings, hihat, or vocals are cancelling out! 2BC multiCORR combines the useful and beloved functions of our free 2BusControl monitor controller plug–in with a carefully designed, third octave multiband correlation meter. Our multiband approach warns you not to overdo stereo spread with your fancy spreading tool, or when your stereo mics are delivering a signal with too much out–of–phase content. Either way, you’d get cancellation when your mix is summed to mono.
Correlation measures the degree of relatedness between left and right channel. If they’re alike, that’s mono, and they will have perfect correlation. Stereo noise is decorrelated, with no similarity between channels. Stereo music should be more like the former, with a bit of “stereoness” to create a soundstage, whereas convincing, diffuse reverb should have lower inter–channel correlation. When content is present in one channel, and an inverted phase version is in the other channel, that sums to zero in mono and the audio disappears.
More info here: MAAT | 2BC multiCORR