Convert log-power-spectrum bins to MFCC using the 'legacy'
    Sphinx transform

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