correlate.py 文件源码

def _filter_resp(freqmin, freqmax, corners=2, zerophase=False, sr=None,
                 N=None, whole=False):
    """
    Complex frequency response of Butterworth-Bandpass Filter.

    :param freqmin: Pass band low corner frequency.
    :param freqmax: Pass band high corner frequency.
    :param corners: Filter corners
    :param zerophase: If True, apply filter once forwards and once backwards.
        This results in twice the number of corners but zero phase shift in
        the resulting filtered trace.
    :param sr: Sampling rate in Hz.
    :param N,whole: passed to scipy.signal.freqz

    :return: frequencies and complex response
    """
    df = sr
    fe = 0.5 * df
    low = freqmin / fe
    high = freqmax / fe
    # raise for some bad scenarios
    if high > 1:
        high = 1.0
        msg = "Selected high corner frequency is above Nyquist. " + \
              "Setting Nyquist as high corner."
        log.warning(msg)
    if low > 1:
        msg = "Selected low corner frequency is above Nyquist."
        raise ValueError(msg)
    [b, a] = iirfilter(corners, [low, high], btype='band',
                       ftype='butter', output='ba')
    freqs, values = freqz(b, a, N, whole=whole)
    if zerophase:
        values *= np.conjugate(values)
    return freqs, values