import array


def lerp_double_rate(iterable):
    """Double rate with linear interpolation"""
    fil = array.array('h', iterable)
    fil.append(0)
    lerp1 = ((a, (a + b) // 2)
             for (a, b) in zip(fil[:-1], fil[1:]))
    return array.array('h', (s for r in lerp1 for s in r))