Subject:Re: Detection of harmonics and rhythmic structureFrom:"James W. Beauchamp" <j-beauch(at)UX1.CSO.UIUC.EDU>Date:Thu, 11 May 2000 16:09:50 -0500Brian Gygi wrote: >Does anyone know some good algorithms for determining a) the presence or >absence of harmonics in a signal (non-speech), and b) whether the signal >is discrete or rhythmic (repetitive)? I can imagine that these two >questions are related, one is in the frequency domain and one in the time >domain. I have fooled around with autocorrelations, but want to be able >to extract a number that would capture the amount of either harmonic or >rhythmic structure in a signal. You could try looking at the autocorrelation function for the spectrum and rms amplitude functions. I.e., In the frequency domain: 1) produce a copy of the spectrum shifted by a frequency increment 2) multiply the original and shifted spectrum. 3) average over frequency and index and save result 4) repeat steps 1-3 5) plot result vs. index 6) if there is a pronounced peak in the graph, it corresponds to the pitch of the harmonics; if there is no pronounced peak, must be no harmonics. In the time domain: 1) compute the rms amplitude vs. time of the signal 2) do the same thing as the frequency domain by replacing frequency by time. 3) a pronouced peak would correspond to the period of repetition; if there is no pronouced peak, there must be no repetition. This is a simple-minded approach, and I'm sure there are more sophisticated algorithms, but it is a start. Jim Beauchamp University of Illinois at Urbana-Champaign j-beauch(at)uiuc.edu

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