I am looking to filter the human voice from enviornmental noise (engine/machinery noise). I was doing some digging and the human voice is between 300 and 10,000 Hz, unfortunatly some of the engine noise is in the same frequency. I could build a bandpass filter and at least eliminate some of the low and high frequency noise but how do you filter noise that is in the same frequency as the signal that you want? Would you have to hook up a mic to a network analyser to see what the specific frequency of the machinery is and then apply a notch filter? And accept that certian tones of voice (no pun inteneded) would be truncated? I have heard there are advanced statistical filters but I have no idea how these work and how well they really work as an active filter.