Do You Know What Your Phase Meter Is Telling You?
Checking stereo mixes for mono playback is easier when you have phase or correlation metering in your DAW or console, but what do the numbers mean?
While someone once pointed out that “life isn’t mono compatible”, the rise of smart speakers has seen a big return to mono playback in recent years, and the need for mono compatibility isn’t going anywhere soon. Most of us use a mono button or plugin to do a listening check to listen for problems, but phase correlation meters let us see the relationship between channels whilst mixing in stereo.
What Are We Listening Out For?
For the uninitiated, pressing the mono button (or plugin) sums L and R and routes it to each speaker so L = L+R and R = L+R. When mono has been compromised things will sound ‘hollow’, ‘sucked-out’, or just wrong when the mono button is pressed.
When both channels are completely in phase they are said to be “fully correlated”. An example of this would be a single mic recording of any source panned centrally. Pressing the mono button will make no difference, meaning all is well.
If both channels are different, such as in a fully wide stereo mic pair, if all is well, both channels will remain audible when the mono button is pressed, but there will be a change in timbre. Such signals are uncorrelated to some extent.
If, for any reason, correlated signals are not at the same point in their swing in both channels, they are said to not be fully in phase. Pressing the mono button will result in a drop in level, or no level at all depending on the amount of offset. In the context of a whole mix, this last scenario can sometimes arise only at certain frequencies owing to the relationship between wavelength and mic spacing in the case of stereo pairs.
What Do The Meter Numbers Mean?
Phase is a big subject that you can learn more about here. Regardless of mono or stereo, a phase or correlation meter shows the overall amount of total phase offset between channels, either in degrees, or on a scale of -1 to +1. On a good day, an entire mix or solo’d source will be anywhere between fully right (+1), and centre (0). On a bad day, the needle will veer to the left of centre, or even fully left when something is wrong.
Out of phase (left of scale) vs. in phase
Does It Matter?
Yes, assuming that your mixes need to translate across a variety of playback systems, a mono check is a good idea along with other objective quality checks leaving you to concentrate on the creative side. Knowing your meter is knowing what will happen before you press the button.
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