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I am searching for the algorithm that takes (audio) signal as an input and outputs weighted intensity of the frequencies of some narrow band (axis X) in time (axis Y). Frequency in the middle of that band would have highest weight.

In other words: It is like spectrograph but I am interested only for the weighted average of small band on X axis where middle of that band would have highest weight. And to have it as function of the time.

Another try: I am looking for an algorithm that computes weighted average of frequencies intensity from narrow band in spectrograph.

I don't know if this algorithm has some specific name. I think it would include some FFT and other "magic".

The best would be to have a link to some (java) library that can do that.

I am total newbie in signal processing so please be more verbose.

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    $\begingroup$ It sounds like you're looking for an answer that is a single, time-varying intensity. I think what you want is a regular band-pass filter (to select only the range of frequencies you're interested in) followed by an energy detector (e.g. sum of the squared signal values within a sliding time window). Using an FFT seems like overkill. $\endgroup$ – dpwe Jul 11 '14 at 3:16
  • $\begingroup$ dpwe, thanks for the advice. btw i don't understand the reason of the downvote. $\endgroup$ – Martin Ždila Jul 11 '14 at 8:04

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