When I mix Studio One (126.96.36.199910 Win x64) in my studio, I route the outputs through either a FireStudio Tube or a Grace Design m108 interface back to my studio monitors. In that setup, I get good stereo separation and am able to flip between mono/stereo mixes with the typical reduction in stereo image, but retention of all key elements in the mix (I just use mono to double check for phasing and overall eq issues).
However, I recently started trying to use my laptop headphone jack with a pair of Audio Technica ATH-M50x headphones to mix when I'm away from the studio and realized that the stereo mixes have a VERY different sound than what I was getting in the studio. When listening in stereo, all of the "side" information gets pushed forward and all of the 'mid' information gets pushed back. Switching to mono brings the 'mid' information back and all the levels are where they're supposed to be. I'm using the ASIO4ALL v2.13 driver as the "audio interface" output for Studio One in this case.
I thought maybe this was just a problem with my mixes, so I imported a professionally-mastered, commercial stereo reference track into Studio One and the same thing is happening to this track. All of the lead vocals and other 'mid' information drops out and all of the hard-panned 'side' information (verbs and guitars, etc.) comes WAAY forward until I switch to mono, then everything levels out.
I then turned off Studio One and opened up Windows Media Player to listen to other commercial tracks and the same thing is happening, which tells me that it's not just Studio One, it's not the ASIO4ALL driver, and it might be my headphone jack or sound card?
Any ideas on why this is happening?
Could it be an impedance issue with the headphones? Some sort of phase cancellation? If that were true, I would think the problem would be worse in mono, not stereo.