Here’s how to read a correlation meter and why it matters.
A correlation meter has a maximum of +1 and a minimum of -1 on its scale. It is usually a needle meter or a bar graph. It is telling you the phase relation of your music.
A good stereo image is centered at 0. Think of this as your ultimate stereo sound. This is where there are true “dual mono” inputs. In other words, this is when the left channel and right are operating independently and have no sounds or frequencies that are in both left and right at the same time. The left and right channels are 90° out of phase with each other so they are not canceling each other out nor summing with each other (mono).
The meter will also read 0 when there is no signal present or when there is only a left or a right signal present (but not both).
A mono image is always at +1. This is when the same signal appears in both the left and right channels. There is no stereo when the meter reads “+1.”
Typically, you want the meter to be bouncing around between 0 and +1. This means that some of your signal is mono and some is stereo. This is what a normal track should have. Yes, it can have some bounces into the -1 region, but it shouldn’t live there. If you notice it in the area between 0 and -1 a lot then you may have some phase cancelation problems (some of your instruments may be canceling out others in various frequencies). If you do have any kind of cancelation or your music is seeing mostly negative on the correlation scale, then I suggest trying the Melda MAutoAlign plugin to shift the phase of the instruments automatically. Or, listening and flipping the phase manually can work also but needs some trial and error. Often, competing instruments just need to be delayed by some milliseconds in order to not be out of phase with others, and this can be tricky to accomplish. Another thing that can help is to send your bass frequencies to mono below a certain frequency (117 Hz for me).
When the left and right cancel each other out completely, the meter reads “-1.” This means the right channel is 180° out of phase with the left. If you hear pulsing in your music at certain frequencies, this could be what is happening.
I use the Brainworx bx_meter because it is simple to use and accurate. Below is a video showing one of my completed tracks played through this meter.