From Sound On Sound (seems appropriate for folks who are questioning if dephase would actually do anything on a single mic capture):
Phase Considerations For Single-mic Recordings
Given that sound takes roughly a millisecond to travel a foot, it's easy to see how recording the same instrument with more than one mic can quickly lead to phase-cancellation problems if the mics are at different distances from the sound source. However, even if all we ever did in the studio was record with a single mic, phase cancellation would still affect our recording because of the way sound reflects from solid surfaces such as walls. For example, if you close-mic an electric guitar cabinet, a significant minority of the sound picked up will actually be reflections from the floor. If the distance from the cabinet's speaker cone is only six inches, and the floor is a foot below the mic, the direct and reflected sounds of the cone will meet at the mic capsule with around 1.5ms delay between them. In theory this will give a comb-filtering effect with total phase cancellation at around 300Hz, 900Hz, 1.5kHz, 2.1kHz, and so on.
But it doesn't work out exactly like this, for a number of reasons. For a start, the reflected sound will almost certainly have a slightly different timbre by virtue of the sound-absorption characteristics of the floor. Sonic reflections will also arrive at the mic capsule off-axis, which will alter their frequency balance. Then there's the contribution made by reflections from other nearby surfaces, which further complicate the frequency-response anomalies. However, even though you don't get a perfect comb-filtering effect in practice, reflections from the floor are still an important contributor to the sound of a close-miked cab, and many producers experiment with lifting and angling cab in relation to the floor for this reason. If you want to hear this for yourself, surf over to my article on guitar recording at
www.soundonsound.com/sos/aug07/ articles/guitaramprecording.htm and have a listen to the audio files in the 'Room & Positioning' box, which demonstrate how much difference moving the cab relative to room boundaries can make.
Of course, phase cancellation between direct and reflected sound can cause problems when recording any instrument, and with acoustic instruments it becomes, if anything, more troublesome — listeners tend to have a less concrete expectation of how an electric guitar should sound, so phase cancellation can be used to shape the tone to taste, whereas with acoustic instruments the listener tends to have clearer expectations, so the tonal effects of comb-filtering are usually less acceptable. Fortunately, it's not too difficult to avoid problems like this, as long as you try to keep performers and microphones at least a few feet from room boundaries and other large reflective surfaces. This can be a bit trickier where space is limited, in which case it can also help to use soft furnishings or acoustic foam to intercept the worst of the room reflections. Our extensive DIY acoustics feature in SOS December 2007 (
Room For Improvement) has lots of useful advice if you find yourself in this situation. Another thing to try in smaller rooms is boundary mics, because their design gets around the phase-cancellation problems associated with whichever surface they're mounted on.
https://www.soundonsound.com/sos/apr08/articles/phasedemystified.htm