def _norm2x(xp, xrange, xcenter):
    """ Convert normalized x in (-1, 1) back to data x unit

    Arguments
        xp: float | np1darray       in (-1, 1)
        xrange: float               MHz
        xcenter: float              MHz

    Returns
        x: float | np1darray
    """

    return xp / 2 * xrange + xcenter