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From Carsten Kr├╝ger <C.Krue...@gmx.org>
Subject [math] transform - fft documentation bug? proposal window function & sonogram
Date Mon, 03 Dec 2007 13:45:03 GMT
Hello,

the class documentation[1] of fft states
"We require the length of data set to be power of 2"
and the method documenation[1] this
"Perform the base-4 Cooley-Tukey FFT algorithm (including inverse)."

One must be wrong:
base-4 alogrithm means that the length of data has to be power of 4

fft without window function is pretty useless, it would be nice to
implement typical[2] window functions for example:
-Hamming
-Hann
-Blackman
-Trinangle
-Rectangle
-Welch
-Gaussian

after having fft and windowfunction, sonogram/spectrogram[3] would be
nice and is easy to implement (10 lines of matlab code).
for example:
public double[][] sonogram (int fftsize, int overlap_factor, int windowfunction)

greetings
Carsten

[1]
http://commons.apache.org/math/apidocs/org/apache/commons/math/transform/FastFourierTransformer.html

[2]
http://en.wikipedia.org/wiki/Window_function

[3]
http://en.wikipedia.org/wiki/Spectrogram


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