audiosoftware
I would like to use my Mac as an audio cancelling device, like headphones that reproduce the outside noise in inverted form, so it cancels out (typically found in airports). With a normal pair of headphones, my Mac could record the ambient noise and send it to my headphones to achieve noise reduction.
Is there a program able to do this?
Returning to this question several years later, it's still a pretty sad state of affairs. The only reliable answer is some sort of hardware solution.
In practice, this is what I ended up buying:
It works really well; you connect the jack to a voice recorder and put the earbud in your ear, which has a microphone and sits between your ear and the phone's speaker. The quality isn't bad (albeit not broadcast quality) and the ability to use an external voice recorder means I'm not having to deal with moving files off my phone or expend extra battery power on a recording app.
That said, this looks really interesting (Though I'm unsure whether you just connect it to your phone and use normally, or whether you connect some sort of hands-free headset to the other side):
http://thenextweb.com/gadgets/2014/05/12/15-quirky-gadgets-accessories-buy-today-2/2/
Considering the question is ultimately about finding a cheap or free software-based recording solution, I'll leave it open in case anyone comes up with something workable.
If your amplifier in your Mac is making audible noises, you should take it in for service. These very new machines should all be under warranty and at the genius bar, they should be able to test your headphones on another Mac and your Mac to be sure yours is normal.
Many audiophile insist on external DAC when there is noise from the CPU or other components since many properly built and functioning computers have noisy amplifiers. Yours should be as good as the rest of the population but perhaps no better than the rest. Just like all LCD displays are not perfect, there are some things you just have to live with, but without hearing your specific Mac it's hard to tell if your expectations are too high or if your hardware is less performant than a typical Mac of that design.
The best way to get Apple to examine any problem is to ask them to examine your specific problem. Especially if you can show noise being generated no matter the signal being played - that would point to a faulty amplifier / grounding issue / crosstalk interference issue as opposed to a problem with a particular music file or genre of music and the Digital-to-Analog chipset that was chosen by Apple. A repair or swap can fix the former, but you can't expect them to redesign the line if you don't like how it was made in the first place.
Best Answer
Audacity can do this as far as I know. There is a White Noise generator, and under the Effects menu there is a "Noise Removal" option.
I don't know if you can do it in realtime, but you could make a short recording of the ambient noise, run the Noise Removal, figure out what got removed (subtract before and after), and then play that part but inverted. Maybe....