After watching the first game of the FIFA worldcup I was very annoyed by the sound of the Vuvuzelas. A theoretical question came up about filtering that noise out of the sound stream.
What algorithms are needed to remove such a "constant" noise and is it possible to keep the quality of other background sounds?
Well, you could do it very easily if you had a live secondary microphone only/mostly picking up the vuvuzelas (i.e. how noise-canceling headphones work). Or, you could identify the frequency signature of the vuvuzelas from a sample, you could loop and counter that with destructive interference. It would not be as effective as the live version, of course.