The Correlation Meter gauges the phase relationship of a stereo signal. The Correlation Meter’s scale values indicate the following:
A +1 correlation value indicates that the left and right channels correlate 100%. In other words, the left and right signals are in phase and are the same shape.
Correlation values in the blue zone (between +1 and the middle position) indicate that the stereo signal is mono compatible.
The middle position indicates the highest allowable amount of left/right divergence, which is often audible as an extremely wide stereo effect.
When the Correlation Meter moves into the red area to the left of the center position, out-of-phase material is present. This leads to phase cancelations if the stereo signal is combined into a mono signal.