fig, ax = plt.subplots()
M = librosa.feature.melspectrogram(y=y, sr=sr)
M_db = librosa.power_to_db(M, ref=np.max)
img = librosa.display.specshow(M_db, y_axis='mel', x_axis='time', ax=ax)
ax.set(title='Mel spectrogram display')
fig.colorbar(img, ax=ax, format="%+2.f dB")