Re: Extremely precise sonogram ?

There’s something more than time and frequency overlap :

Time-frequency “reassignment” that AlexHarker pointed :

“Compared with the classic spectrogram (aka ‘waterfall’) display, reassigned spectrograms can offer better resolution in the time- as well as in the frequency domain. (…) by comparing the phase between two neighbouring frequency bins (within the same STFT) it is possible to relocate the energy from that cell along the time(!) axis. By comparing the phase in a frequency bin (between two neighbouring STFTs), it is possible to relocate the energy from that cell along the frequency(!) axis.” http://www.qsl.net/dl4yhf/speclab/ra_spectrogram.htm http://www.nbb.cornell.edu/neurobio/land/PROJECTS/ReassignFFT/index.html

“the method of reassignment sharpens blurry time-frequency data by relocating the data according to local estimates of instantaneous frequency and group delay.” http://en.wikipedia.org/wiki/Reassignment_method

By checking the “Enable reassignment” box in Izotope RX while using time&frequency overlaps, you can get fine pitch tracking like in the first image below from a singing female voice (“shafqat.aif” cnmat audio example), far better than standard FFT without overlap (2nd image).

The wavelet window software didn’t really convinced me about wavelets finally, plus it is damned slow. I find FFT with reassignment and overlaps more precise than wavelets.

(By the way, RavenPro also have time and frequency overlaps option, but it is lost behind hundreds of option, i just found it in “configure spectrogram”.)

[attachment=128487,297] [attachment=128487,298]

Attachments:
  1. StandardFFT-without-overlaps.jpg
Mar 29, 2010 at 9:54pm #176922