Actually there are TWO topics here, first Absolute Phase of both channels and relative phase of ONE channel.
While Absolute Phase of both channels may be poorly understood, and some or many people can't even tell ( and I think I'm among those ) I'm still waiting to be wow'd hearing a really noticeable change by reversing the phase at both speakers. Considering that there is a story that on many LP's and CD's the Absolute Phase is changed on odd and even cuts, or randomly, if that is true... I guess there is no set rule for Absolute Phase.
The other point, Stereo Channel Relative Phase - The aforementioned Phase Switch that David refers to as found on Early Preamps, and Integrated Amps... was used to reverse
One Channel's Phase while
not affecting the other Stereo Channel. There exist many early Stereo recordings, Reel Tapes and LP's where either one channel is out of phase with the other, or some tracks of a multitrack recording, are out of phase with others. Been documented, supposedly.
So there is Inverting, or Non-Inverting Absolute Phase, and there is Stereo Channel Relative Phase.
-Steven L. Bender
Is/was there any industry standard regarding phase?
I am assuming here, but my guess would be that there was no standard for polarity in the industry either for manufacturers or recording companies, or else early pre-amps by Marantz, McIntosh, Harmon Kardon, and a host of others would never have installed a phase reverse switch.
I use the switch all the time to check recordings. I have found that some Columbia and Everest classical vinyl releases can benefit from reversing phase on playback. Also, multi-track recordings can have the singer in phase and the musicians reversed.
Some modern pre-amps will tell you if they are phase inverting. My Conrad Johnson PV-5 is non-inverting. And now, some of the new high end pre-amps have phase switching on them once again.
David