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<section id="ducking-py-adjust-the-gain-of-a-signal-based-on-the-presence-of-another-one">
<h1>02-ducking.py - Adjust the gain of a signal based on the presence of another one.<a class="headerlink" href="#ducking-py-adjust-the-gain-of-a-signal-based-on-the-presence-of-another-one" title="Permalink to this heading">¶</a></h1>
<p>Ducking is an audio effect commonly used in radio. In ducking, the
level of one audio signal is reduced by the presence of another signal.</p>
<p>Here we use a Follower object to track the RMS envelope of the voice signal. Then
we use an audio conditional to create a switch, whose value is 1 when the voice is
talking and 0 when it is silent. This signal is finally used to change the amplitude
of the music whenever the voice is talking.</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="c1"># Alternate voice and silence.</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/tables.html#pyo.SndTable" title="pyo.lib.tables.SndTable"><span class="n">table</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/tables.html#pyo.SndTable" title="pyo.lib.tables.SndTable"><span class="n">SndTable</span></a><span class="p">(</span><span class="n">SNDS_PATH</span> <span class="o">+</span> <span class="s2">"/transparent.aif"</span><span class="p">)</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/effects.html#pyo.SDelay" title="pyo.lib.effects.SDelay"><span class="n">metro</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/effects.html#pyo.SDelay" title="pyo.lib.effects.SDelay"><span class="n">SDelay</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/triggers.html#pyo.Metro" title="pyo.lib.triggers.Metro"><span class="n">Metro</span></a><span class="p">(</span><span class="mi">3</span><span class="p">)</span><span class="o">.</span><span class="n">play</span><span class="p">(),</span> <span class="mi">1</span><span class="p">)</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/triggers.html#pyo.TrigEnv" title="pyo.lib.triggers.TrigEnv"><span class="n">voice</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/triggers.html#pyo.TrigEnv" title="pyo.lib.triggers.TrigEnv"><span class="n">TrigEnv</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/effects.html#pyo.SDelay" title="pyo.lib.effects.SDelay"><span class="n">metro</span></a><span class="p">,</span> <a class="sphinx-codeautolink-a" href="../../api/classes/tables.html#pyo.SndTable" title="pyo.lib.tables.SndTable"><span class="n">table</span></a><span class="p">,</span> <span class="n">dur</span><span class="o">=</span><span class="n">table</span><span class="o">.</span><span class="n">getDur</span><span class="p">(),</span> <span class="n">mul</span><span class="o">=</span><span class="mf">0.7</span><span class="p">)</span>
<span class="n">stvoice</span> <span class="o">=</span> <span class="n">voice</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="o">.</span><span class="n">out</span><span class="p">()</span>
<span class="c1"># Play some music-box style tune!</span>
<span class="n">freqs</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/functions/conv.html#pyo.midiToHz" title="pyo.midiToHz"><span class="n">midiToHz</span></a><span class="p">([</span><span class="mi">60</span><span class="p">,</span> <span class="mi">62</span><span class="p">,</span> <span class="mi">64</span><span class="p">,</span> <span class="mi">65</span><span class="p">,</span> <span class="mi">67</span><span class="p">,</span> <span class="mi">69</span><span class="p">,</span> <span class="mi">71</span><span class="p">,</span> <span class="mi">72</span><span class="p">])</span>
<span class="n">choice</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/randoms.html#pyo.Choice" title="pyo.lib.randoms.Choice"><span class="n">Choice</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/randoms.html#pyo.Choice" title="pyo.lib.randoms.Choice"><span class="n">choice</span></a><span class="o">=</span><span class="n">freqs</span><span class="p">,</span> <span class="n">freq</span><span class="o">=</span><span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">])</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.Port" title="pyo.lib.filters.Port"><span class="n">port</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.Port" title="pyo.lib.filters.Port"><span class="n">Port</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/randoms.html#pyo.Choice" title="pyo.lib.randoms.Choice"><span class="n">choice</span></a><span class="p">,</span> <span class="n">risetime</span><span class="o">=</span><span class="mf">0.001</span><span class="p">,</span> <span class="n">falltime</span><span class="o">=</span><span class="mf">0.001</span><span class="p">)</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/generators.html#pyo.SineLoop" title="pyo.lib.generators.SineLoop"><span class="n">sines</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/generators.html#pyo.SineLoop" title="pyo.lib.generators.SineLoop"><span class="n">SineLoop</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.Port" title="pyo.lib.filters.Port"><span class="n">port</span></a><span class="p">,</span> <span class="n">feedback</span><span class="o">=</span><span class="mf">0.05</span><span class="p">)</span>
<span class="n">music</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/pan.html#pyo.SPan" title="pyo.lib.pan.SPan"><span class="n">SPan</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/generators.html#pyo.SineLoop" title="pyo.lib.generators.SineLoop"><span class="n">sines</span></a><span class="p">,</span> <span class="n">pan</span><span class="o">=</span><span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mf">0.2</span><span class="p">,</span> <span class="mf">0.8</span><span class="p">,</span> <span class="mf">0.5</span><span class="p">],</span> <span class="n">mul</span><span class="o">=</span><span class="mf">0.1</span><span class="p">)</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="c1"># Follow voice RMS amplitude.</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/triggers.html#pyo.TrigEnv" title="pyo.lib.triggers.TrigEnv"><span class="n">voice</span></a><span class="p">,</span> <span class="n">freq</span><span class="o">=</span><span class="mi">10</span><span class="p">)</span>
<span class="c1"># talk = 1 if voice is playing and 0 if not.</span>
<span class="n">talk</span> <span class="o">=</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> <span class="mf">0.005</span>
<span class="c1"># Smooth the on/off signal (rising is faster than falling)...</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.Port" title="pyo.lib.filters.Port"><span class="n">amp</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.Port" title="pyo.lib.filters.Port"><span class="n">Port</span></a><span class="p">(</span><span class="n">talk</span><span class="p">,</span> <span class="n">risetime</span><span class="o">=</span><span class="mf">0.05</span><span class="p">,</span> <span class="n">falltime</span><span class="o">=</span><span class="mf">0.1</span><span class="p">)</span>
<span class="c1"># ... then rescale it (1 when no voice and 0.1 when voice is playing).</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/utils.html#pyo.Scale" title="pyo.lib.utils.Scale"><span class="n">ampscl</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/filters.html#pyo.Port" title="pyo.lib.filters.Port"><span class="n">amp</span></a><span class="p">,</span> <span class="n">outmin</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">outmax</span><span class="o">=</span><span class="mf">0.1</span><span class="p">)</span>
<span class="c1"># Display the gain factor.</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/analysis.html#pyo.Scope" title="pyo.lib.analysis.Scope"><span class="n">sc</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/analysis.html#pyo.Scope" title="pyo.lib.analysis.Scope"><span class="n">Scope</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/utils.html#pyo.Scale" title="pyo.lib.utils.Scale"><span class="n">ampscl</span></a><span class="p">)</span>
<span class="c1"># Apply gain factor and output music.</span>
<span class="n">outsynth</span> <span class="o">=</span> <span class="p">(</span><span class="n">music</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">ampscl</span></a><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>
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