使用scipy的butter带通滤波器时报错：
RuntimeWarning: invalid value encountered in reduce ret = umr_sum(arr, axis, dtype, out, keepdims)
RuntimeWarning: overflow encountered in reduce ret = umr_sum(arr, axis, dtype, out, keepdims)
RuntimeWarning: invalid value encountered in subtract ext = np.concatenate((2 * left_end - left_ext,
RuntimeWarning: invalid value encountered in subtract 2 * right_end - right_ext),ext = np.concatenate((2 * left_end - left_ext,
RuntimeWarning: overflow encountered in multiply ext = np.concatenate((2 * left_end - left_ext,
解决方法：
滤波器阶数取得太高导致的，降低滤波器阶数即可