17th September 2008 - 08:08 PM
Neither did I understand the question. And by the way, what do you call a "db equipment"?
Distinguish sounds and noises one from another: this is very complicated! I would say: not a single hope nowadays in the general case. One wouldn't even know how to define what is one sort of sound and what is a different sort.
What does commonly exist for over two decades is put microphones at several places in a room where you expect sound and noise sources, and subtract the signals very precisely so that unwanted noise sources are wiped from the desired signal.
The typical use (if not the only one...) is in a broadcasting studio where the speaker has a microphone, and the air conditioner (or any source with a precise location) another. The air conditioner noise is then subtracted from the broadcast signal.
This needs a very exact subtraction, as the human ear wants at least 20dB improvement and rather 50dB. Worse, noise propagation from the source to the speaker's microphone varies in time, for instance when people move in the room. Propagation also depends heavily on the frequency.
The answer is called an adaptive filter, as it adapts its response in real time by "measuring" (difficult) how much of the noise gets into the useful signal. The standard method is a "Kalman filter".
Have a look athttp://en.wikipedia.org/wiki/Kalman_filter