How to deal with phase problems?

I'm glad; you ask!

Sometime, musicchamber, even when you've reversed polarity on a mic more was needed.

Coincidently, osiseau, from my very first post at this forum, I tried to make phase problems or their cancellations enough of a concern that could warrant eventual attention from forum and staff members alike, but, who maybe were enough interested to just find an immediate solution, that is, a remedy to the potential problems  —not much unlike your own. 

See numbered eleventh (11) of my initial entry under the topic: New features you want to Pianoteq (not instruments).

Though by this time individual note volume adjustments had already been long offered, I suggested still you ought to have ways to direct them independently into separate outputs, meaning anytime you were in need of convenient ways to avoid unpleasant phase cancellations between the two (2) or more microphones pointed at a piano and as often as cancellations occur a lot of professional mixers needs ways to continuously get around the potential cancellations.  Which could result (unfavorably) in frequency dropouts.

However since you can recently divide in PIANOTEQ any piano into distinct layers —with each having a different designated output— and the piano instrument emanating throughout sound coming from its one half going to one of the outputs and from the other half yet to another, at least theoretically, undesirable phase cancellation within the software becomes easily avoided.  (That’s only if half the notes comes from one output when the other half comes from another.)

I've yet to try out this theory however.

Whenever I need to record any piano as a solo instrument inside my DAW very handy to me are nearby software solutions I can quickly grab, notably MAuto Stereo Fix and MAuto Align from MeldaProduction and of course Pi from Sound Radix.  Also, InPhase from Waves I had gotten on hand but it requiring an updated plan —an extra expense— puts it now way out of my reach.  I'm hardly ever going again to try and go toward that one!

Anyway trial copies of all of these (linked) are available, anytime you'd just like to delve into them!

If you do dig one of the suggestions more than the others, just let know…

Specifically about MAuto Align, you seemingly have to load that like any other similar type of phase related plugin placed on a couple of mono tracks instead of some stereo track normally you'd use to put any plugin as an instance; as it specifically needs to always align one track to another entirely separate track or a combination of many even such used in a drum kit recording.

Obviously oiseau, as you suggest problematic phase nowadays is relatively little of an issue and little ever if it is in fact at all.  Wholeheartedly I agree with you; that it is —whether or not vaguely noticeable— a sign of the times.

(Phase however problematic just seems as a topic to come surely with the modern blues of today and of course classics of yesterday, when yet it only as phase cancellation might cause listeners to lament over recorded performances, some of the highly noted accomplishments out of the works of the masters.  To an ardent engineer, who is enterprising and adept on listeners' feelings and emotions, it just may have well assured its proper place amongst the very saddest of the songs ever recorded.)

Technically, people the consumers who listen to music today appear addicted to the misalignments which result out of phase cancellations.  Presently, phase incoherence is much a part of any engineer's strategy as you'd think phase coherence; it's often by design his well thought out choice.  Which a producer of a song necessarily could want.

I just listened to "A Time for Love" and "Love Theme from 'Spartacus'" both recorded performances of the late Bill Evans.  They two appear highly processed though with lots of phase cancellations perhaps intentional on the part of an obviously talented engineer.

Imagine what might had happened, possibly, if PIANOTEQ were available at the time of his recording!

Anyway, at this thread I'm planning to post a very recent recording I just engineered that has absolutely no phase cancellations in it anywhere.  It's a modern rendition of counterpoint played at a piano though like a rollercoaster ride filled with times of sheer happiness and alarmingly utter sadness, depression and cynicism.

Until I post that (here) maybe look over one I did before at: Engineering Pianoteq Steinway B Close Mic Preset.

Allow me to elaborate:

I've a current solo piano recording that I loaded as a MIDI software instance, PIANOTEQ PRO, onto a stereo instrument track inside Apple Logic Pro.

Very easily I could had instantiated PIANOTEQ to output mono, LCRS or other various choices of Multi-Output instead of stereo, if at anytime I preferred another to the latter (stereo) my obvious choice in Logic.

While the PIANOTEQ PRO copy utilizes a stereo track, I must place MAuto Align on a corresponding Audio FX slot that's specifically duo mono, if I'm going to have that plugin properly align any note timing which is from one of the mics timed essentially to the occurrence of the exact same note but coming from the other microphone.

Whenever PIANOTEQ has a stereo output formed by two (2) microphones selected and I needed to use MAuto Align to stop any possible microphone delay directly, that could come from PIANOTEQ when used in a DAW, I am certain to use again the MAuto Align plugin since still it can treat each mic as a separate mono source and as long as it itself was loaded only as a dual mono effect.  That corresponds or affects separately each mic on my solo piano (PIANOTEQ) instance though both mics have been added together to form the stereo image of the single instance.

Have to say no, oiseau, since it can work as one instance only Duo Mono (at least in Logic).  (Smile.)

If however you do load the plugin as a stereo instance, that might mean your intention is simply to purposely preserve your instrument's delay or stereo psychoacoustics and keep that virtually untouched between its two (2) mics, or subsequently add and align very simply a third, fourth or fifth, to it still maintained and intact —however without necessarily any extra delay contributed from yet additional microphone placement injected into the stereo field, or visa-versa.

Although PIANOTEQ includes capable means including COMPENSATION, LEVEL, DELAY and polarity reversed —indicated by the color red— that can help you to cope with notes in or out of phase with others, sometimes I personally prefer to try out specialized plugins in a DAW, which will offer somehow different approaches to similarly compensate.  (PIANOTEQ has confined adjustments to phase coherence to static singularly 180° phase rotations.)

Pi from Sound Radix continually adjusts rotations to whatever degrees necessary, and anytime so needed.

MAuto Stereo Fix as suggested earlier is also a plugin that can look over the complete duration of a stereo recording and arrive at a more favorable fix to any potentially faulty misplacement of the mics, and, especially anytime you've left some delay intentionally inside your recording.  (Apparently it analyzes for loudness, delay, spectrum and phase coherence {polarity rotation}.)  Delay specifically it adjusts by volume changes as you can enter whatever tolerance in decibels desirable throughout your recording.

On my own recent stereo solo piano recording I used MAuto Stereo Fix to cover loudness over the entire span of my recording, MAuto Align to align automatically the two distinguishable signals from its stereo paired mics, and lastly —just before a limiter on a master I placed— Pi to have automatic and consistent rotations of phase in correlation to the two (2) mic signals, which have resultantly been corrected.

So, in conclusion:

When one way, oiseau, to deal with phase results in a net outcome that's not quite what you've anticipated, man make haste to another!