</p>
<ul>
<li>the <span style="background-color:black; color:white;">transfer function</span> in white,</li>
- <li>the <span style="background-color:black; color:red;">phase response</span> in red (optionnal),</li>
+ <li>the <span style="background-color:black; color:red;">phase response</span> in red (optional),</li>
<li>the <span style="background-color:black; color:green;">post effect spectrum</span> in green.</li>
</ul>