How does noise cancellation work in android?

Question

I came across this relatively old post which describes how impressively Nexus One's noise cancellation works and I was wondering where can I find more information about its implementation in the OS software.

In particular:

1. How much of it is done using software and how much of it is done in hardware?
2. Which modules in the Android source code are responsible for noise cancellation?
3. Can I control its behavior via Android's API? (if so, which ones)
4. Does it also work with the microphone in the headset that comes with Nexus One (4-pin 3.5mm jack) or does it work with the built-in microphone only?

Answer 1

I only know the answer for the Nexus One, but:

1. It's done in hardware.
2. Not sure.
3. Nope.
4. Maybe?

For the N1, it works using a second microphone in the back, and comparing the two signals. I don't know exactly how this process is done (hardware or software), but I know there isn't an API for it. Also, it probably doesn't work for the external headset, since there's no second sound source to compare the first one to (unless the headset has two mics too, but I don't think it does).