dd order filter is use to ensure a 0dB response at DC (see TMW Technical Solution <a href="http://www.mathworks.com/support/solutions/data/1-2YWEQD.html?solution=1-2YWEQD">1-2YWEQD</a>). The algorithm designs a filter of the highest order possible to meet these condiditons. If such a filter can not be designed you will need to decimate in stages e.g.  by 10, then 10 again to achieve downsampling by a factor of 100.</p>
    </blockquote>
  </li>
  <li>Second, downsampling is performed by taking every Nth 