ion</a>
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            <li class="nav-item" data-level="3"><a href="#example-2-frequency-modulation-with-envelops" class="nav-link">Example 2: frequency modulation with envelops</a>
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            </li>
              </ul>
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              </ul>
            </li>
            
            <li class="nav-item" data-level="1"><a href="#further-readings" class=