preprocess.py 文件源码

def _decimate(x, q):
    """
    Downsample the signal after low-pass filtering to avoid aliasing.
    An order 16 Chebyshev type I filter is used.

    Parameters
    ----------
    x : ndarray
        The signal to be downsampled, as an N-dimensional array.
    q : int
        The downsampling factor.

    Returns
    -------
    y : ndarray
        The down-sampled signal.
    """
    if not isinstance(q, int):
        raise TypeError("q must be an integer")

    b, a = signal.filter_design.cheby1(16, 0.025, 0.98 / q)

    y = signal.filtfilt(b, a, x, axis=-1)

    sl = [slice(None)] * y.ndim
    sl[-1] = slice(None, None, q)
    return y[sl]