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Fonction buttord - module scipy.signal

Signature de la fonction buttord

def buttord(wp, ws, gpass, gstop, analog=False, fs=None) 

Description

buttord.__doc__

Butterworth filter order selection.

    Return the order of the lowest order digital or analog Butterworth filter
    that loses no more than `gpass` dB in the passband and has at least
    `gstop` dB attenuation in the stopband.

    Parameters
    ----------
    wp, ws : float
        Passband and stopband edge frequencies.

        For digital filters, these are in the same units as `fs`. By default,
        `fs` is 2 half-cycles/sample, so these are normalized from 0 to 1,
        where 1 is the Nyquist frequency. (`wp` and `ws` are thus in
        half-cycles / sample.) For example:

            - Lowpass:   wp = 0.2,          ws = 0.3
            - Highpass:  wp = 0.3,          ws = 0.2
            - Bandpass:  wp = [0.2, 0.5],   ws = [0.1, 0.6]
            - Bandstop:  wp = [0.1, 0.6],   ws = [0.2, 0.5]

        For analog filters, `wp` and `ws` are angular frequencies (e.g., rad/s).
    gpass : float
        The maximum loss in the passband (dB).
    gstop : float
        The minimum attenuation in the stopband (dB).
    analog : bool, optional
        When True, return an analog filter, otherwise a digital filter is
        returned.
    fs : float, optional
        The sampling frequency of the digital system.

        .. versionadded:: 1.2.0

    Returns
    -------
    ord : int
        The lowest order for a Butterworth filter which meets specs.
    wn : ndarray or float
        The Butterworth natural frequency (i.e. the "3dB frequency"). Should
        be used with `butter` to give filter results. If `fs` is specified,
        this is in the same units, and `fs` must also be passed to `butter`.

    See Also
    --------
    butter : Filter design using order and critical points
    cheb1ord : Find order and critical points from passband and stopband spec
    cheb2ord, ellipord
    iirfilter : General filter design using order and critical frequencies
    iirdesign : General filter design using passband and stopband spec

    Examples
    --------
    Design an analog bandpass filter with passband within 3 dB from 20 to
    50 rad/s, while rejecting at least -40 dB below 14 and above 60 rad/s.
    Plot its frequency response, showing the passband and stopband
    constraints in gray.

    >>> from scipy import signal
    >>> import matplotlib.pyplot as plt

    >>> N, Wn = signal.buttord([20, 50], [14, 60], 3, 40, True)
    >>> b, a = signal.butter(N, Wn, 'band', True)
    >>> w, h = signal.freqs(b, a, np.logspace(1, 2, 500))
    >>> plt.semilogx(w, 20 * np.log10(abs(h)))
    >>> plt.title('Butterworth bandpass filter fit to constraints')
    >>> plt.xlabel('Frequency [radians / second]')
    >>> plt.ylabel('Amplitude [dB]')
    >>> plt.grid(which='both', axis='both')
    >>> plt.fill([1,  14,  14,   1], [-40, -40, 99, 99], '0.9', lw=0) # stop
    >>> plt.fill([20, 20,  50,  50], [-99, -3, -3, -99], '0.9', lw=0) # pass
    >>> plt.fill([60, 60, 1e9, 1e9], [99, -40, -40, 99], '0.9', lw=0) # stop
    >>> plt.axis([10, 100, -60, 3])
    >>> plt.show()