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Fonction spectrogram - module scipy.signal

Signature de la fonction spectrogram

def spectrogram(x, fs=1.0, window=('tukey', 0.25), nperseg=None, noverlap=None, nfft=None, detrend='constant', return_onesided=True, scaling='density', axis=-1, mode='psd') 

Description

spectrogram.__doc__

Compute a spectrogram with consecutive Fourier transforms.

    Spectrograms can be used as a way of visualizing the change of a
    nonstationary signal's frequency content over time.

    Parameters
    ----------
    x : array_like
        Time series of measurement values
    fs : float, optional
        Sampling frequency of the `x` time series. Defaults to 1.0.
    window : str or tuple or array_like, optional
        Desired window to use. If `window` is a string or tuple, it is
        passed to `get_window` to generate the window values, which are
        DFT-even by default. See `get_window` for a list of windows and
        required parameters. If `window` is array_like it will be used
        directly as the window and its length must be nperseg.
        Defaults to a Tukey window with shape parameter of 0.25.
    nperseg : int, optional
        Length of each segment. Defaults to None, but if window is str or
        tuple, is set to 256, and if window is array_like, is set to the
        length of the window.
    noverlap : int, optional
        Number of points to overlap between segments. If `None`,
        ``noverlap = nperseg // 8``. Defaults to `None`.
    nfft : int, optional
        Length of the FFT used, if a zero padded FFT is desired. If
        `None`, the FFT length is `nperseg`. Defaults to `None`.
    detrend : str or function or `False`, optional
        Specifies how to detrend each segment. If `detrend` is a
        string, it is passed as the `type` argument to the `detrend`
        function. If it is a function, it takes a segment and returns a
        detrended segment. If `detrend` is `False`, no detrending is
        done. Defaults to 'constant'.
    return_onesided : bool, optional
        If `True`, return a one-sided spectrum for real data. If
        `False` return a two-sided spectrum. Defaults to `True`, but for
        complex data, a two-sided spectrum is always returned.
    scaling : { 'density', 'spectrum' }, optional
        Selects between computing the power spectral density ('density')
        where `Sxx` has units of V**2/Hz and computing the power
        spectrum ('spectrum') where `Sxx` has units of V**2, if `x`
        is measured in V and `fs` is measured in Hz. Defaults to
        'density'.
    axis : int, optional
        Axis along which the spectrogram is computed; the default is over
        the last axis (i.e. ``axis=-1``).
    mode : str, optional
        Defines what kind of return values are expected. Options are
        ['psd', 'complex', 'magnitude', 'angle', 'phase']. 'complex' is
        equivalent to the output of `stft` with no padding or boundary
        extension. 'magnitude' returns the absolute magnitude of the
        STFT. 'angle' and 'phase' return the complex angle of the STFT,
        with and without unwrapping, respectively.

    Returns
    -------
    f : ndarray
        Array of sample frequencies.
    t : ndarray
        Array of segment times.
    Sxx : ndarray
        Spectrogram of x. By default, the last axis of Sxx corresponds
        to the segment times.

    See Also
    --------
    periodogram: Simple, optionally modified periodogram
    lombscargle: Lomb-Scargle periodogram for unevenly sampled data
    welch: Power spectral density by Welch's method.
    csd: Cross spectral density by Welch's method.

    Notes
    -----
    An appropriate amount of overlap will depend on the choice of window
    and on your requirements. In contrast to welch's method, where the
    entire data stream is averaged over, one may wish to use a smaller
    overlap (or perhaps none at all) when computing a spectrogram, to
    maintain some statistical independence between individual segments.
    It is for this reason that the default window is a Tukey window with
    1/8th of a window's length overlap at each end.

    .. versionadded:: 0.16.0

    References
    ----------
    .. [1] Oppenheim, Alan V., Ronald W. Schafer, John R. Buck
           "Discrete-Time Signal Processing", Prentice Hall, 1999.

    Examples
    --------
    >>> from scipy import signal
    >>> from scipy.fft import fftshift
    >>> import matplotlib.pyplot as plt
    >>> rng = np.random.default_rng()

    Generate a test signal, a 2 Vrms sine wave whose frequency is slowly
    modulated around 3kHz, corrupted by white noise of exponentially
    decreasing magnitude sampled at 10 kHz.

    >>> fs = 10e3
    >>> N = 1e5
    >>> amp = 2 * np.sqrt(2)
    >>> noise_power = 0.01 * fs / 2
    >>> time = np.arange(N) / float(fs)
    >>> mod = 500*np.cos(2*np.pi*0.25*time)
    >>> carrier = amp * np.sin(2*np.pi*3e3*time + mod)
    >>> noise = rng.normal(scale=np.sqrt(noise_power), size=time.shape)
    >>> noise *= np.exp(-time/5)
    >>> x = carrier + noise

    Compute and plot the spectrogram.

    >>> f, t, Sxx = signal.spectrogram(x, fs)
    >>> plt.pcolormesh(t, f, Sxx, shading='gouraud')
    >>> plt.ylabel('Frequency [Hz]')
    >>> plt.xlabel('Time [sec]')
    >>> plt.show()

    Note, if using output that is not one sided, then use the following:

    >>> f, t, Sxx = signal.spectrogram(x, fs, return_onesided=False)
    >>> plt.pcolormesh(t, fftshift(f), fftshift(Sxx, axes=0), shading='gouraud')
    >>> plt.ylabel('Frequency [Hz]')
    >>> plt.xlabel('Time [sec]')
    >>> plt.show()