feature selection for classification for rare classes I have a spectrogram of a signal and want to classify it. I used different features such as MFFC, the density of power spectrum and other common features and classify using the random forest, but I did not get good results. 

I think that my features are not well selected and I guess that there is no relation between my aimed classes and the selected features.
my classes are so rare.

could anyone suggest a way for obtaining features?(for very rare data)
also, I used some methods of feature extraction from biological images, but I think that the data are different. my data are double and those are some 3 dimensions data.
Try one of these algorithms for feature selection:

BLogReg
CFS
Chi Square
FCBF
Fisher Score
Gini Index
Information Gain
Kruskal-Wallis
mRMR
Relief-F
SBMLR
T-test
SPEC