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librosa.feature.melspectrogram

librosa.feature.melspectrogram(y=None, sr=22050, S=None, n_fft=2048, hop_length=512, win_length=None, window='hann', center=True, pad_mode='reflect', power=2.0, **kwargs)

Compute a mel-scaled spectrogram.

If a spectrogram input S is provided, then it is mapped directly onto the mel basis by mel_f.dot(S).

If a time-series input y, sr is provided, then its magnitude spectrogram S is first computed, and then mapped onto the mel scale by mel_f.dot(S**power).

By default, power=2 operates on a power spectrum.

Parameters:

ynp.ndarray [shape=(n,)] or None

audio time-series

srnumber > 0 [scalar]

sampling rate of y

Snp.ndarray [shape=(d, t)]

spectrogram

n_fftint > 0 [scalar]

length of the FFT window

hop_lengthint > 0 [scalar]

number of samples between successive frames. See librosa.stft

win_lengthint <= n_fft [scalar]

Each frame of audio is windowed by window(). The window will be of length win_length and then padded with zeros to match n_fft.

If unspecified, defaults to win_length = n_fft.

windowstring, tuple, number, function, or np.ndarray [shape=(n_fft,)]

• a window specification (string, tuple, or number); see scipy.signal.get_window

• a window function, such as scipy.signal.windows.hann

• a vector or array of length n_fft

centerboolean

• If True, the signal y is padded so that frame t is centered at y[t * hop_length].

• If False, then frame t begins at y[t * hop_length]

pad_modestring

If center=True, the padding mode to use at the edges of the signal.

By default, STFT uses reflection padding.

powerfloat > 0 [scalar]

Exponent for the magnitude melspectrogram. e.g., 1 for energy, 2 for power, etc.

kwargsadditional keyword arguments

Mel filter bank parameters.

See librosa.filters.mel for details.

Returns:

Snp.ndarray [shape=(n_mels, t)]

Mel spectrogram

See also

librosa.filters.mel

Mel filter bank construction

librosa.stft

Short-time Fourier Transform

Examples

>>> y, sr = librosa.load(librosa.ex('trumpet'))
>>> librosa.feature.melspectrogram(y=y, sr=sr)
array([[3.837e-06, 1.451e-06, ..., 8.352e-14, 1.296e-11],
       [2.213e-05, 7.866e-06, ..., 8.532e-14, 1.329e-11],
       ...,
       [1.115e-05, 5.192e-06, ..., 3.675e-08, 2.470e-08],
       [6.473e-07, 4.402e-07, ..., 1.794e-08, 2.908e-08]],
      dtype=float32)

Using a pre-computed power spectrogram would give the same result:

>>> D = np.abs(librosa.stft(y))**2
>>> S = librosa.feature.melspectrogram(S=D, sr=sr)

Display of mel-frequency spectrogram coefficients, with custom arguments for mel filterbank construction (default is fmax=sr/2):

>>> # Passing through arguments to the Mel filters
>>> S = librosa.feature.melspectrogram(y=y, sr=sr, n_mels=128,
...                                     fmax=8000)

>>> import matplotlib.pyplot as plt
>>> fig, ax = plt.subplots()
>>> S_dB = librosa.power_to_db(S, ref=np.max)
>>> img = librosa.display.specshow(S_dB, x_axis='time',
...                          y_axis='mel', sr=sr,
...                          fmax=8000, ax=ax)
>>> fig.colorbar(img, ax=ax, format='%+2.0f dB')
>>> ax.set(title='Mel-frequency spectrogram')