.. note::
    :class: sphx-glr-download-link-note

    Click :ref:`here <sphx_glr_download_intro_scipy_auto_examples_plot_spectrogram.py>` to download the full example code
.. rst-class:: sphx-glr-example-title

.. _sphx_glr_intro_scipy_auto_examples_plot_spectrogram.py:


======================================
Spectrogram, power spectral density
======================================

Demo spectrogram and power spectral density on a frequency chirp.



.. code-block:: python


    import numpy as np
    from matplotlib import pyplot as plt







Generate a chirp signal
###########################################################



.. code-block:: python


    # Seed the random number generator
    np.random.seed(0)

    time_step = .01
    time_vec = np.arange(0, 70, time_step)

    # A signal with a small frequency chirp
    sig = np.sin(0.5 * np.pi * time_vec * (1 + .1 * time_vec))

    plt.figure(figsize=(8, 5))
    plt.plot(time_vec, sig)




.. image:: /intro/scipy/auto_examples/images/sphx_glr_plot_spectrogram_001.png
    :class: sphx-glr-single-img




Compute and plot the spectrogram
###########################################################

 The spectrum of the signal on consecutive time windows



.. code-block:: python


    from scipy import signal
    freqs, times, spectrogram = signal.spectrogram(sig)

    plt.figure(figsize=(5, 4))
    plt.imshow(spectrogram, aspect='auto', cmap='hot_r', origin='lower')
    plt.title('Spectrogram')
    plt.ylabel('Frequency band')
    plt.xlabel('Time window')
    plt.tight_layout()





.. image:: /intro/scipy/auto_examples/images/sphx_glr_plot_spectrogram_002.png
    :class: sphx-glr-single-img




Compute and plot the power spectral density (PSD)
###########################################################

 The power of the signal per frequency band



.. code-block:: python


    freqs, psd = signal.welch(sig)

    plt.figure(figsize=(5, 4))
    plt.semilogx(freqs, psd)
    plt.title('PSD: power spectral density')
    plt.xlabel('Frequency')
    plt.ylabel('Power')
    plt.tight_layout()




.. image:: /intro/scipy/auto_examples/images/sphx_glr_plot_spectrogram_003.png
    :class: sphx-glr-single-img





.. code-block:: python


    plt.show()








**Total running time of the script:** ( 0 minutes  0.200 seconds)


.. _sphx_glr_download_intro_scipy_auto_examples_plot_spectrogram.py:


.. only :: html

 .. container:: sphx-glr-footer
    :class: sphx-glr-footer-example



  .. container:: sphx-glr-download

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



  .. container:: sphx-glr-download

     :download:`Download Jupyter notebook: plot_spectrogram.ipynb <plot_spectrogram.ipynb>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.readthedocs.io>`_