Invert ?

 You can hear it. Fortunately, when two signals are badly out of phase, it’s easy to hear. When two similar tracks are mixed, they can sound thinner, tinnier, or harsher, indicating that they have a phase problem.

@yogiboy  Thanks. That makes sense. 

To get a baseline of what phase inversion sounds like, push the invert switch on your preamp for any song you are currently playing and listen if you hear a difference.  If you do, you will know what to listen for in inverted tracks.

That invert switch is a nice feature. My gear does not have that so if I wanted to check out the correct phase I would have to reverse the pos and neg on both speakers. I would have to shut off my amp every time and that’s just not worth the inconvenience of doing that!!

There was a booklet that made the rounds several decades ago, called The Wood Effect. Who knows, it may still be in print, or available through an online book vendor. The topic was absolute phase- and a number of examples were given as I recall. But, as another member here astutely pointed out, most stuff is multi-tracked, often recorded and mixed in various studios, whether all that stuff when mixed down is in the same phase was pretty doubtful. I do remember one example being that old warhorse- Dusty's Look of Love. Was the horn blowing or sucking? (rhetorical music question, not a value judgment). It's one of those quandaries that is probably impossible to solve. 

However, in previous systems, there seemed to be only modest effect by hitting the invert switch. In my current system, I leave it non-inverted and if I hit invert, it does not sound right. I'm not sure what that means, but I just don't mess with it.