Are you listening louder to one or the other…
We perceive pitch differently at different volumes - http://en.wikipedia.org/wiki/Pitch_(music) particular at lower frequencies.
Its a fascinating subject, the ear-brain system isn’t just a measurement device and pitch and frequency are not necessarily the same thing.
Lots of singers will sing sharp when using headphones, to counter this it’s fairly normal to use just one or hold them away from the ear a bit.
Yup I regularly noticed the pitch change when changing from cans to monitors. I think it’s a transient thing.
I think it wouldn’t be a Doppler effect - as far as I know, the Doppler effect is the shift in frequency when the source is moving towards or away from you. So unless you’re mixing from a rocking chair or ceiling-mounted trapeze contraption, must be some other effect!
It’s a known phenomenon where the soundwaves travles throught the bone (bone conduction)of your skull rather than through the front door i.e. your ear (air conduction).
Hi - Any pure distance effect (i.e., without motion of the source) on frequency perception wouldn’t be a Doppler - that’ s strictly a motion-requiring phenomenon. I guess a Leslie speaker would be an example of a Doppler phenomenon in music - moving sound source, making the sound warble a bit.
Stepping outside of my comfort zone for this next sentence, though: The distant sound may likely have a different pitch than an identical source not so remote, as I think higher frequencies don’t travel as well, so there is a natural “distance-based HF roll off” effect; all that being the theory behind moving things “back” on the perceived sound stage - a source can be made to sound farther off by rolling the highs off. If I’m off base on this one, someone please set me straight!
But off the top of my head, I’d question whether the 3 feet distance between headphones and near fields would be enough to “lose” some high frequencies based on distance to be noticeable. I’d guess other factors, like destructive interference when the low frequencies hit the wall behind the nearfields and bounce back towards us, would be more prominent in causing a pitch change.
I’d guess another, much simpler, explanation for pitch differences between near fields and headphones might be … the frequency responses are different between the two systems, so they would be expected to reproduce a sound and its harmonics differently.
All in all, I guess it would be surprising if in all but the best studios and with the most idealized headphones the two did sound the same!
losing high frequencies over distance means you don’t hear them as loud, that’s not the same as a different pitch though. Change in amplitude is different from change in frequency.
I’m not entirely sure but I think frequencies can change when the soundwave travels through a different medium which would explain the skull thing mentioned earlier.
Not being an acoustician, I have to ask - isn’t turning down the loudness of a sound’s high frequency like what we do with our EQs, which changes the perceived pitch of the music?
Oh, I see now … sorry. So the OP wasn’t referring to music, but rather a single pure tone?
I was kind of thinking of all the harmonics of a complex sound…
The trouble may come from the fact that frequency is objective and pitch is purely subjective!
Frequency is a measured value whereas pitch can be ambiguous and is entirly up to the listener to determine and will be affected by all sorts of things, not least the amount of overtones in a complex sound. Not all people are born equal and it is up to your brain to determine just what pitch it thinks it’s hearing!
For example it’s a lot easier to tell a pitch when compared to another, but could you tell a single note is in tune with no other reference tone? (A=440)
For what it’s worth I would never try to determine pitch via headphones, I would always use speakers, just seems to be the more natural way of listening.
You are right, I’m no accoustician either and all my knowledge on this matter comes from me being a mechanical engineer. I’m slowly starting to see that everything I know about signals and frequency response of mechanical systems doesn’t quite carry over to accoustics. 
Split’s above post makes sense though, you can give a frequency (or combination of frequencies) a name (pitch) but that doesn’t say anything about how different people perceive it. I wouldn’t be surprised if pitch is not only a function of your brain, but also of your own ‘biological accoustics’ and maybe even waveform.
@Bredo: I thought I read somewhere that ideally you should monitor at as high levels as possible because then your ear’s frequency response would be as flat as possible. Never did that anyway because I’d rather enjoy listening for a while longer 
My feeling (FWIW) is that is very insightful. I’ve spent what seems like lifetimes micro-comping the “best of the best” (not that any are all that good!), only to find out it sounds … maybe not much better than any given complete take, if at all.
Thinking about what you wrote, I wonder if “micro-comping” only works well for those that are professional singers that are pretty much on pitch (with good phrasing) all the time - only minute adjustments needed - so that stringing together parts from different takes doesn’t sound so unnatural.
For what are probably similar reasons as what you are talking about, I decided not too long ago that I would NOT comp till the cows came home - the search for perfection (“normalized” of course to my limited vocal skills) was taking me forever, the results weren’t all that impressive, and it kept me from moving on with my projects.
I’m now at the stage where I’ve accepted my voice is more Tom Petty/Bob Dylan than Paul McCartney. So my phrases will be off-pitch somewhat, but “real”. Sure, I’ll do some comping, but my goal will be to try to use complete phrases/verses, even if they are not as technically perfect as they could be.
Thanks for sharing that, Steve Fogal - got me thinking!
Consistent change in pitch between the two, or any which way on any given comparison?
How much of a pitch change? Could you play some sine wave pitches out, and use a guitar tuner to see how much?
Very interesting - nice pickup!
I would hazard a guess that the pitch would be the same.