python - 为什么巴特沃斯带通滤波器的边际值如此不切实际地大？

Question

我使用巴特沃斯带通：

def butter_bandpass_prep(lowcut, highcut, fs, order=5):
    """Butterworth bandpass auxilliary function."""
     nyq = 0.5 * fs # Minimal frequency (nyquist criterion)
     low = lowcut / nyq
     high = highcut / nyq
     b, a = sp.signal.butter(order, [low, high], btype='band')
     return b, a

def butter_bandpass(src, lowcut, highcut, fs, order=5):
    """Butterworth bandpass filter."""
    b, a = butter_bandpass_prep(lowcut, highcut, fs, order=order)
    dst = sp.signal.filtfilt(b, a, src)
    return dst

我一般来说它似乎运作良好，但在边缘我总是得到一些不切实际的值。似乎过滤后的边际值下降到零......有没有办法防止这种情况发生？十分感谢！