def mel(sr, n_dft, n_mels=128, fmin=0.0, fmax=None, htk=False, norm=1):
    """[np] create a filterbank matrix to combine stft bins into mel-frequency bins
    use Slaney (said Librosa)

    n_mels: numbre of mel bands
    fmin : lowest frequency [Hz]
    fmax : highest frequency [Hz]
        If `None`, use `sr / 2.0`
    """
    return librosa.filters.mel(sr=sr, n_fft=n_dft, n_mels=n_mels,
                               fmin=fmin, fmax=fmax,
                               htk=htk, norm=norm).astype(K.floatx())
[np] create a filterbank matrix to combine stft bins into mel-frequency bins
    use Slaney (said Librosa)

    n_mels: numbre of mel bands
    fmin : lowest frequency [Hz]
    fmax : highest frequency [Hz]
        If `None`, use `sr / 2.0`
    
asr/models/layers/backend.py