The absolute phase of a given recording may be one or the other, but there is not a consistency from one recording label to another, not even for various recordings from the same label.
Regarding a phase switch, I use a passive controller which has a feature that allows toggling the absolute phase using its remote. This allows instant comparison of the the two phase options.
Why does this matter? When absolute phase is reversed, compression and rarefaction components of the sound waves are reversed. The physical mechanism of the ear does not respond symmetrically to compression and rarefaction in sound waves. This is particularly obvious with bass frequencies. When toggling the phase control, the deep bass is obviously more realistic on one phase setting than the other, with more richness and deeper extension. There are other differences. At the absolute phase setting that has the better bass, there are other differences. Instruments' midrange is better integrated with the bass. The effect is a better balanced, coherent soundstage. Treble is more relaxed. At the opposite phase setting (for that recording) an annoying forwardness or even a slight treble glare shows up.
Recordings of live piano performances are excellent tools to identify how correct/incorrect absolute phase impacts the overall realism. You don't need to crank up the volume to hear differences, but a natural volume level of a live performance is ideal.
It's important that you listen the the absolute phase difference from your listening position. Using my controller's remote to toggle absolute phase makes it the correct setting for a recording immediately clear. If you have to walk over to flip the switch, you will be fighting an uphill battle. Alternating the two candidate settings immediately makes the differences obvious. If you have to use a manual phase switch on the preamp or controller, you may want to consider placing it at arm's reach from you listening chair. Unfortunately, that would probably require longer cable runs which is not desirable.
Hope this helps, Robert
