I wrote a spectral analysis library called udsp:

http://www.eliteraspberries.com/doc/udsp-user-guide.html

https://code.google.com/p/udsp/

In the future it will include:

* support for more FFT libraries, like FFTW;

* some signals processing functions, such as basic frequency modulation/demodulation; and

* a NumPy-compatible Python interface.

Its best feature at the moment is convolution and correlation.