.. _sphx_glr_auto_examples_plot_presets.py:


=======
Presets
=======

This notebook demonstrates how to use the `presets` package to change the
default parameters for librosa.



.. code-block:: python


    # Code source: Brian McFee
    # License: ISC







We'll need numpy and matplotlib for this example



.. code-block:: python

    from __future__ import print_function
    import numpy as np
    import matplotlib.pyplot as plt

    # Import the Preset class
    from presets import Preset


    # To use presets, we'll make a dummy import of librosa
    # and the display submodule here.
    import librosa as _librosa
    import librosa.display as _display
    # The assignment here is to circumvent python's inability
    # to rename submodule imports within the package
    _librosa.display = _display







By default, librosa uses the following parameters across all functions:
  - `sr=22050` (sampling rate)
  - `hop_length=512` (number of samples between frames)
  - `n_fft=2048` (number of samples per frame in STFT-like analyses)

You may want to change these values to suit your application, but
doing so consistently in every function call can be somewhat cumbersome.

Presets makes it easy to do this all at once by wrapping the module
and all function calls, and overriding default arguments.



.. code-block:: python


    # First, we need to set up the preset-wrapped librosa import

    librosa = Preset(_librosa)

    # To change the default sampling rate, we can set the `sr` entry:
    librosa['sr'] = 44100

    # and similarly for hop_length and n_fft
    librosa['hop_length'] = 1024
    librosa['n_fft'] = 4096

    # In general, when you set `librosa['X']` for any string `X`, anywhere within
    # librosa where the parameter `X` occurs as a keyword-argument,
    # its default value will be replaced by whatever value you provide.







Now we can load in a file and do some analysis with the new defaults



.. code-block:: python

    filename = 'audio/Karissa_Hobbs_-_09_-_Lets_Go_Fishin.mp3'

    y, sr = librosa.load(filename, duration=5, offset=35)

    # Generate a Mel spectrogram:

    M = librosa.feature.melspectrogram(y=y)

    # Of course, you can still override the new default manually, e.g.:

    M_highres = librosa.feature.melspectrogram(y=y, hop_length=512)


    # And plot the results
    plt.figure(figsize=(6, 6))
    ax = plt.subplot(3, 1, 1)

    librosa.display.specshow(librosa.power_to_db(M, ref=np.max),
                             y_axis='mel', x_axis='time')

    plt.title('44100/1024/4096')

    plt.subplot(3, 1, 2, sharex=ax, sharey=ax)
    librosa.display.specshow(librosa.power_to_db(M_highres, ref=np.max),
                             hop_length=512,
                             y_axis='mel', x_axis='time')
    plt.title('44100/512/4096')

    # We can repeat the whole process with different defaults, just by
    # updating the parameter entries
    librosa['sr'] = 11025

    y2, sr2 = librosa.load(filename, duration=5, offset=35)
    M2 = librosa.feature.melspectrogram(y=y2, sr=sr2)

    plt.subplot(3, 1, 3, sharex=ax, sharey=ax)
    librosa.display.specshow(librosa.power_to_db(M2, ref=np.max),
                             y_axis='mel', x_axis='time')

    plt.title('11025/1024/4096')

    plt.tight_layout()
    plt.show()



.. image:: /auto_examples/images/sphx_glr_plot_presets_001.png
    :align: center




**Total running time of the script:** ( 0 minutes  1.027 seconds)



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     :download:`Download Python source code: plot_presets.py <plot_presets.py>`



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