You can display a mono-compatibility meter in the Channel Meters window, Hardware Meters window, and Record dialog to detect correlations or differences between the channels of a file that can cause phase cancellation when downmixing to mono.

Right-click the meters and choose Show Mono-Compatibility Meter from the shortcut menu to toggle the display of the mono-compatibility meter.

• When the channels are similar, the right (or top) half of the meter is illuminated:
  

• When the channels exhibit phase cancellations, the left (or bottom) half of the meter is illuminated:
  

Mono-Compatibility Meter