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<section id="rms-tracing-py-auto-wah-effect">
<h1>04-rms-tracing.py - Auto-wah effect.<a class="headerlink" href="#rms-tracing-py-auto-wah-effect" title="Permalink to this heading">¶</a></h1>
<p>The auto-wah effect (also know as “envelope following filter”) is like a
wah-wah effect, but instead of being controlled by a pedal, it is the RMS
amplitude of the input sound which control it. The envelope follower (RMS)
is rescaled and used to change the frequency of a bandpass filter applied
to the source.</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <a class="sphinx-codeautolink-a" href="../../api/alphabetical.html#module-pyo" title="pyo"><span class="nn">pyo</span></a> <span class="kn">import</span> <span class="o">*</span>
<span class="n">s</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/server.html#pyo.Server" title="pyo.lib.server.Server"><span class="n">Server</span></a><span class="p">()</span><span class="o">.</span><span class="n">boot</span><span class="p">()</span>
<span class="n">MINFREQ</span> <span class="o">=</span> <span class="mi">250</span>
<span class="n">MAXFREQ</span> <span class="o">=</span> <span class="mi">5000</span>
<span class="c1"># Play the drum lopp.</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/players.html#pyo.SfPlayer" title="pyo.lib.players.SfPlayer"><span class="n">sf</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/players.html#pyo.SfPlayer" title="pyo.lib.players.SfPlayer"><span class="n">SfPlayer</span></a><span class="p">(</span><span class="s2">"../snds/drumloop.wav"</span><span class="p">,</span> <span class="n">loop</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="c1"># Follow the amplitude envelope of the input sound.</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/analysis.html#pyo.Follower" title="pyo.lib.analysis.Follower"><span class="n">follow</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/analysis.html#pyo.Follower" title="pyo.lib.analysis.Follower"><span class="n">Follower</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/players.html#pyo.SfPlayer" title="pyo.lib.players.SfPlayer"><span class="n">sf</span></a><span class="p">)</span>
<span class="c1"># Scale the amplitude envelope (0 -> 1) to the desired frequency</span>
<span class="c1"># range (MINFREQ -> MAXFREQ).</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/utils.html#pyo.Scale" title="pyo.lib.utils.Scale"><span class="n">freq</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/utils.html#pyo.Scale" title="pyo.lib.utils.Scale"><span class="n">Scale</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/analysis.html#pyo.Follower" title="pyo.lib.analysis.Follower"><span class="n">follow</span></a><span class="p">,</span> <span class="n">outmin</span><span class="o">=</span><span class="n">MINFREQ</span><span class="p">,</span> <span class="n">outmax</span><span class="o">=</span><span class="n">MAXFREQ</span><span class="p">)</span>
<span class="c1"># Filter the signal with a band pass. Play with the Q to make the</span>
<span class="c1"># effect more or less present.</span>
<span class="nb">filter</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.ButBP" title="pyo.lib.filters.ButBP"><span class="n">ButBP</span></a><span class="p">(</span><span class="n">sf</span><span class="o">.</span><span class="n">mix</span><span class="p">(</span><span class="mi">2</span><span class="p">),</span> <span class="n">freq</span><span class="o">=</span><a class="sphinx-codeautolink-a" href="../../api/classes/utils.html#pyo.Scale" title="pyo.lib.utils.Scale"><span class="n">freq</span></a><span class="p">,</span> <span class="n">q</span><span class="o">=</span><span class="mi">2</span><span class="p">)</span><span class="o">.</span><span class="n">out</span><span class="p">()</span>
<span class="n">s</span><span class="o">.</span><span class="n">gui</span><span class="p">(</span><span class="nb">locals</span><span class="p">())</span>
</pre></div>
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