noise cancellation of non-repetitive noise There are a new noise cancellation headphones that almost fully cancel human noise. 

What kinds of algorithms could achieve that ?

EDIT:by human noise , i mean talking. In general, previous audio cancellation headphones didn't work that well for attenuating talking.
Since I cannot comment, here comes a short answer.

As far as I know, there are microphones outside the earphone. The microphones record the outside noise and generate sounds with 180 phase shift to cancel the noises. The noises are canceled actively.