.. include:: /project-links.txt
.. include:: /abbreviation.txt

.. getthecode:: find-pitch.py
    :language: python

======================================
 Find the Pitch of a Vibrating String
======================================
This example shows how to find the pitch of a guitare string using a spectral analysis.

.. code-block:: python

    import os
    
    import numpy as np
    import matplotlib.pyplot as plt
    
    from Musica.Audio.AudioFormat import AudioFormat
    

We load a wav file containing a recording of a E2 guitar string.

.. code-block:: python

    wav_path = os.path.join(os.path.dirname(__file__), '..', '..',
                            'data', 'string-waves', 'clean', 'E2.1.wav')
    audio = AudioFormat.open(wav_path)
    
    figure1 = plt.figure(1, (20, 10))
    axe = plt.subplot(111)
    data = audio.channel(0, as_float=True)
    axe.plot(data)
    axe.set_title('E2 Guitare String')
    axe.set_xlabel('Time [t]')
    axe.set_ylabel('Amplitude')
    


.. image:: data.png
  :align: center


.. code-block:: python

    spectrum = audio.spectrum(0, number_of_samples=2**16)
    
    figure2 = plt.figure(1, (20, 10))
    axe = plt.subplot(111)
    axe.grid()
    #? axe.plot(spectrum.values)
    # axe.semilogx(spectrum.frequencies, spectrum.magnitude)
    axe.semilogx(spectrum.frequencies, spectrum.decibel_power)
    #? axe.semilogx(spectrum.frequencies, spectrum.h_dome(20), 'o-')
    axe.set_title('Spectrum')
    axe.set_xlabel('Frequencies [Hz]')
    axe.set_ylabel('Power [db]')
    


.. image:: spectrum.png
  :align: center


.. code-block:: python

    figure3 = plt.figure(1, (20, 10))
    axe = plt.subplot(111)
    frequencies, hfs = spectrum.hfs(5)
    axe.semilogx(frequencies, hfs, 'o-')
    axe.grid()
    axe.set_title('Harmonic Product Spectrum')
    axe.set_xlabel('Frequencies [Hz]')
    axe.set_ylabel('Amplitude')
    


.. image:: hfs.png
  :align: center


.. code-block:: python

    i_max = np.argmax(hfs)
    string_frequency = frequencies[i_max]
    frequency_error = spectrum.frequency_resolution
    # print('Frequency: {:.1f} +- {:.1f} Hz'.format(string_frequency, frequency_error))
    

String frequency = 82.8 +- 0.7 Hz

.. code-block:: python

    plt.tight_layout()
    plt.show()