def _proc(tr, sampling_rate=10):
    """
    Basic processing including downsampling, detrend, and demean.

    :param tr: raw trace
    :param sampling_rate:
    :return tr: trace after processing
    """
    # deep copy
    tr2 = tr.copy()
    tr2.interpolate(sampling_rate)
    tr2.detrend(type="linear")
    tr2.detrend(type="demean")
    return tr2