code: def logspec2s2mfc(logspec, ncep=13):
      
      nframes, nfilt = logspec.shape
      melcos = s2dctmat(nfilt, ncep, 1./nfilt)
      return numpy.dot(logspec, melcos.T) / nfilt
docs: Convert log-power-spectrum bins to MFCC using the 'legacy'
      Sphinx transform