Re: Sound Analysis Tools (James Beauchamp )

Subject: Re: Sound Analysis Tools
From:    James Beauchamp  <jwb(at)TIMBRE.MUSIC.UIUC.EDU>
Date:    Fri, 17 Nov 1995 13:13:11 -0600

On Fri Nov 17 10:11:35 1995) Thierry Rochebois wrote: >What I have is a frequency sampled gaussian. >On a log scale a gaussian is a parabola. >So, the quadratic interpolation of this spectrum on a log scale gives >an accurate value of the frequency and amplitude. We are using a Kaiser window. Isn't a Kaiser close to a guassian? After all true guassians would require infinite time and frequency windows. >For each frame I store the frequency, phase and amplitude for each peak >of the spectrum (ie for every sine wave). >Before resynthesis, I select the peaks that correspond to harmonics >(thanks to an harmony criterion). We've had good results using this approach for harmonic sounds. We have a pitch detector program that makes this possible for variable fundamentals within a limited search range. However, the program sometimes makes mistakes. Also, one must decide on a threshold for the tracking method, and this can cause problems. For sounds of fixed pitch, I have had better and more consistent results using a pitch-synchronous phase vocoder program. Also, more recently I've been interested in tracking inharmonic partials of percussion sounds, which the McAulay-Quatieri method can accomplish as long as the partials are not too close together. Chime tones work well for example, except the resynthesized attacks are a bit mushy. Cymbals and drums are another story. I haven't figured out a way to stretch them using this approach without introducing artifacts. I feel that the key is to latch onto the correct modal frequencies. Again on Fri, 17 Nov 1995 19:08:51 +0100) Thierry Rochebois wrote: >After extracting the harmonic part from the signal, I can study the signal >with other time frequency/resolution tradeoff. This can be efficient to study >transients (high time resolution, low frequency resolution). This is important. Two comments: 1) Most musical signals can tolerate a fair amount of phase distortion if it is fixed. Witness what happens when we play back in a room. Room modes cause all kinds of phase distortion. But preserving the correct phases is very important for subtraction in the time domain. 2) We shouldn't restrict ourselves to harmonics. Any well-defined partials could be in the primary (non-residue) part of the signal. Incidentally, the software I use for analysis, graphics, modification, and synthesis on Unix workstations is available for FTP. Anyone who is interested in a copy can contact me, and I will give you the acquisition information. Jim James Beauchamp professor of music and electrical & computer engineering 2136 Music Bldg. MC-056, University of Illinois at Urbana-Champaign, 1114 W. Nevada, Urbana, IL 61801 email: j-beauch(at) phone: +1-217-244-1207/344-3307 fax: +1-217-244-4585 WWW:

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