Module « scipy.signal »

Fonction cheb1ord - module scipy.signal

Signature de la fonction cheb1ord

def cheb1ord(wp, ws, gpass, gstop, analog=False, fs=None) 

Description

cheb1ord.__doc__

Chebyshev type I filter order selection.

    Return the order of the lowest order digital or analog Chebyshev Type I
    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 Chebyshev type I filter that meets specs.
    wn : ndarray or float
        The Chebyshev natural frequency (the "3dB frequency") for use with
        `cheby1` to give filter results. If `fs` is specified,
        this is in the same units, and `fs` must also be passed to `cheby1`.

    See Also
    --------
    cheby1 : Filter design using order and critical points
    buttord : 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 a digital lowpass filter such that the passband is within 3 dB up
    to 0.2*(fs/2), while rejecting at least -40 dB above 0.3*(fs/2). Plot its
    frequency response, showing the passband and stopband constraints in gray.

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

    >>> N, Wn = signal.cheb1ord(0.2, 0.3, 3, 40)
    >>> b, a = signal.cheby1(N, 3, Wn, 'low')
    >>> w, h = signal.freqz(b, a)
    >>> plt.semilogx(w / np.pi, 20 * np.log10(abs(h)))
    >>> plt.title('Chebyshev I lowpass filter fit to constraints')
    >>> plt.xlabel('Normalized frequency')
    >>> plt.ylabel('Amplitude [dB]')
    >>> plt.grid(which='both', axis='both')
    >>> plt.fill([.01, 0.2, 0.2, .01], [-3, -3, -99, -99], '0.9', lw=0) # stop
    >>> plt.fill([0.3, 0.3,   2,   2], [ 9, -40, -40,  9], '0.9', lw=0) # pass
    >>> plt.axis([0.08, 1, -60, 3])
    >>> plt.show()