Not having ever looked at our FFT code, I won't address the issue of whether
the documentation is right or wrong (I suspect the documentation simply has a
typo; base-2 FFT's are the easiest to implement, given that they're the only
kind anyone ever seems to write about, so I can't believe we have a base-4
implementation, which would be less easily usable).
I'm +1 on providing window functions, given how commonly needed they are. I'm
-0 on the spectrogram, having personally spent time trying to use a naive
spectrogram as a power spectrum estimator. I only spent enough time on that
task to come to the understanding that it wasn't as simple as it seemed it
should be. Maybe even that understanding is wrong. In any case, I would
prefer that the package provide a function that "does what most people think of
when thinking about a spectrogram" rather than the naive spectrogram. Unless
my understanding, as I mentioned, is wrong and the naive spectrogram is
actually useful.
Al
--
Albert Davidson Chou
Get answers to Mac questions at http://www.Mac-Mgrs.org/ .
----- Original Message ----
From: Carsten Krüger <[EMAIL PROTECTED]>
To: dev@commons.apache.org
Sent: Monday, December 3, 2007 5:45:03 AM
Subject: [math] transform - fft documentation bug? proposal window function &
sonogram
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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