This should be done using the fortran methods from the FFTW3 API described in (http://www.fftw.org/doc/1d-Real_002deven-DFTs-_0028DCTs_0029.html) ### More info: [fftw discrete cosine transform](http://www.variousconsequences.com/2009/05/fftw-discrete-cosine-transform.html) [Lecture notes](http://wiki.scinethpc.ca/wiki/images/8/8c/SCLecture8.pdf) [Speech recognition](http://arxiv.org/pdf/1204.5841.pdf)