maad.sound.median_equalizer

maad.sound.median_equalizer(Sxx, display=False, savefig=None, **kwargs)

Remove background noise in spectrogram using median equalizer.

Parameters:

Sxx2D numpy array

Original spectrogram (or image), !!! not in dB

displayboolean, optional, default is False

Display the signal if True

savefigstring, optional, default is None

Root filename (with full path) is required to save the figures. Postfix is added to the root filename.

kwargs, optional. This parameter is used by plt.plot and savefig functions

• savefilenamestr, optional, default :’_spectro_after_noise_subtraction.png’

  Postfix of the figure filename

• figsizetuple of integers, optional, default: (4,10)

  width, height in inches.

• titlestring, optional, default‘Spectrogram’

  title of the figure

• xlabelstring, optional, default‘Time [s]’

  label of the horizontal axis

• ylabelstring, optional, default‘Amplitude [AU]’

  label of the vertical axis

• cmapstring or Colormap object, optional, default is ‘gray’

  See https://matplotlib.org/examples/color/colormaps_reference.html in order to get all the existing colormaps examples: ‘hsv’, ‘hot’, ‘bone’, ‘tab20c’, ‘jet’, ‘seismic’, ‘viridis’…

• vmin, vmaxscalar, optional, default: None

  vmin and vmax are used in conjunction with norm to normalize luminance data. Note if you pass a norm instance, your settings for vmin and vmax will be ignored.

• extentscalars (left, right, bottom, top), optional, default: None

  The location, in data-coordinates, of the lower-left and upper-right corners. If None, the image is positioned such that the pixel centers fall on zero-based (row, column) indices.

• dpiinteger, optional, default is 96

  Dot per inch. For printed version, choose high dpi (i.e. dpi=300) => slow For screen version, choose low dpi (i.e. dpi=96) => fast

• formatstring, optional, default is ‘png’

  Format to save the figure

… and more, see matplotlib

Returns:

Sxx_out2d ndarray of scalar

Spectrogram after denoising

References

[1]

This function has been proposed first by Carol BEDOYA <carol.bedoya@pg.canterbury.ac.nz> Adapted by S. Haupert Oct 9, 2018 for Python

Examples

Load audio recording and convert it into spectrogram

>>> s, fs = maad.sound.load('../data/rock_savanna.wav')
>>> Sxx,tn,fn,ext = maad.sound.spectrogram (s, fs)   

Convert linear spectrogram into dB

>>> Sxx_dB = maad.util.power2dB(Sxx) +96

Remove stationnary noise from the spectrogram

>>> Sxx_noNoise = maad.sound.median_equalizer(Sxx)
>>> Sxx_dB_noNoise =  maad.util.power2dB(Sxx_noNoise) 

Plot both spectrograms

>>> import matplotlib.pyplot as plt 
>>> import numpy as np
>>> fig, (ax1, ax2) = plt.subplots(2, 1)
>>> maad.util.plot2d(Sxx_dB, ax=ax1, extent=ext, title='original', vmin=np.median(Sxx_dB), vmax=np.median(Sxx_dB)+40)
>>> maad.util.plot2d(Sxx_dB_noNoise, ax=ax2, extent=ext, title='Without stationary noise',vmin=np.median(Sxx_dB_noNoise), vmax=np.median(Sxx_dB_noNoise)+40)
>>> fig.set_size_inches(15,8)
>>> fig.tight_layout()