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<section id="bandpass-filters-py-narrowing-a-bandpass-filter-bandwidth">
<h1>02-bandpass-filters.py - Narrowing a bandpass filter bandwidth.<a class="headerlink" href="#bandpass-filters-py-narrowing-a-bandpass-filter-bandwidth" title="Permalink to this heading">¶</a></h1>
<p>This example illustrates the difference between a simple IIR second-order
bandpass filter and a cascade of second-order bandpass filters. A cascade
of four bandpass filters with a high Q can be used as a efficient resonator
on the signal.</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"># White noise generator</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/generators.html#pyo.Noise" title="pyo.lib.generators.Noise"><span class="n">n</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/generators.html#pyo.Noise" title="pyo.lib.generators.Noise"><span class="n">Noise</span></a><span class="p">(</span><span class="mf">0.5</span><span class="p">)</span>
<span class="c1"># Common cutoff frequency control</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/controls.html#pyo.Sig" title="pyo.lib._core.Sig"><span class="n">freq</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/controls.html#pyo.Sig" title="pyo.lib._core.Sig"><span class="n">Sig</span></a><span class="p">(</span><span class="mi">1000</span><span class="p">)</span>
<span class="n">freq</span><span class="o">.</span><span class="n">ctrl</span><span class="p">([</span><a class="sphinx-codeautolink-a" href="../../api/classes/map.html#pyo.SLMap" title="pyo.lib._maps.SLMap"><span class="n">SLMap</span></a><span class="p">(</span><span class="mi">50</span><span class="p">,</span> <span class="mi">5000</span><span class="p">,</span> <span class="s2">"lin"</span><span class="p">,</span> <span class="s2">"value"</span><span class="p">,</span> <span class="mi">1000</span><span class="p">)],</span> <span class="n">title</span><span class="o">=</span><span class="s2">"Cutoff Frequency"</span><span class="p">)</span>
<span class="c1"># Common filter's Q control</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/controls.html#pyo.Sig" title="pyo.lib._core.Sig"><span class="n">q</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/controls.html#pyo.Sig" title="pyo.lib._core.Sig"><span class="n">Sig</span></a><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
<span class="n">q</span><span class="o">.</span><span class="n">ctrl</span><span class="p">([</span><a class="sphinx-codeautolink-a" href="../../api/classes/map.html#pyo.SLMap" title="pyo.lib._maps.SLMap"><span class="n">SLMap</span></a><span class="p">(</span><span class="mf">0.7</span><span class="p">,</span> <span class="mi">20</span><span class="p">,</span> <span class="s2">"log"</span><span class="p">,</span> <span class="s2">"value"</span><span class="p">,</span> <span class="mi">5</span><span class="p">)],</span> <span class="n">title</span><span class="o">=</span><span class="s2">"Filter's Q"</span><span class="p">)</span>
<span class="c1"># Second-order bandpass filter</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.Reson" title="pyo.lib.filters.Reson"><span class="n">bp1</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.Reson" title="pyo.lib.filters.Reson"><span class="n">Reson</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/generators.html#pyo.Noise" title="pyo.lib.generators.Noise"><span class="n">n</span></a><span class="p">,</span> <a class="sphinx-codeautolink-a" href="../../api/classes/controls.html#pyo.Sig" title="pyo.lib._core.Sig"><span class="n">freq</span></a><span class="p">,</span> <span class="n">q</span><span class="o">=</span><a class="sphinx-codeautolink-a" href="../../api/classes/controls.html#pyo.Sig" title="pyo.lib._core.Sig"><span class="n">q</span></a><span class="p">)</span>
<span class="c1"># Cascade of second-order bandpass filters</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.Resonx" title="pyo.lib.filters.Resonx"><span class="n">bp2</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.Resonx" title="pyo.lib.filters.Resonx"><span class="n">Resonx</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/generators.html#pyo.Noise" title="pyo.lib.generators.Noise"><span class="n">n</span></a><span class="p">,</span> <a class="sphinx-codeautolink-a" href="../../api/classes/controls.html#pyo.Sig" title="pyo.lib._core.Sig"><span class="n">freq</span></a><span class="p">,</span> <span class="n">q</span><span class="o">=</span><a class="sphinx-codeautolink-a" href="../../api/classes/controls.html#pyo.Sig" title="pyo.lib._core.Sig"><span class="n">q</span></a><span class="p">,</span> <span class="n">stages</span><span class="o">=</span><span class="mi">4</span><span class="p">)</span>
<span class="c1"># Interpolates between input objects to produce a single output</span>
<span class="n">sel</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/pan.html#pyo.Selector" title="pyo.lib.pan.Selector"><span class="n">Selector</span></a><span class="p">([</span><a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.Reson" title="pyo.lib.filters.Reson"><span class="n">bp1</span></a><span class="p">,</span> <a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.Resonx" title="pyo.lib.filters.Resonx"><span class="n">bp2</span></a><span class="p">])</span><span class="o">.</span><span class="n">out</span><span class="p">()</span>
<span class="n">sel</span><span class="o">.</span><span class="n">ctrl</span><span class="p">(</span><span class="n">title</span><span class="o">=</span><span class="s2">"Filter selector (0=Reson, 1=Resonx)"</span><span class="p">)</span>
<span class="c1"># Displays the spectrum contents of the chosen source</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/analysis.html#pyo.Spectrum" title="pyo.lib.analysis.Spectrum"><span class="n">sp</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/analysis.html#pyo.Spectrum" title="pyo.lib.analysis.Spectrum"><span class="n">Spectrum</span></a><span class="p">(</span><span class="n">sel</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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