<p>
  The LTPDA toolbox contains a class (<tt>pzmodel</tt>) for creating and using pole/zero models. 
  The <it>pole/zero model helper GUI</it> allows the user to visualise the pole/zero model as it's
  being designed. It also allows the user to quickly see how the corresponding IIR filter 
  (<tt>miir</tt> object) will look for different sample rates.
</p>	
<p>
  To start the pole/zero model helper:
  <div class="fragment">
    <pre>
      >> pzmodel_helper
</pre>
  </div>
  or click the appropriate button on the LTPDA Launch Bay.
</p>
<p>
  Once the GUI is loaded, you will see the following figure:
</p>
<br>
<img src="images/pzmodel_helper.png" alt="pzmodel helper" border="3">
<br>
<p>
  You can add poles and zeros to the model by entering the frequency (and Q) in the edit boxes, then click
  <tt>Add pole</tt> or <tt>Add zero</tt> as appropriate. The response is then updated in the response axes.   
</p>
<br>
<img src="images/pzmodel_helper_eg1.png" alt="pzmodel helper" border="3">
<br>