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<section id="lowpass-filters-py-the-effect-of-the-order-of-a-filter">
<h1>01-lowpass-filters.py - The effect of the order of a filter.<a class="headerlink" href="#lowpass-filters-py-the-effect-of-the-order-of-a-filter" title="Permalink to this heading">¶</a></h1>
<p>For this first example about filtering, we compare the frequency
spectrum of three common lowpass filters.</p>
<ul class="simple">
<li><p>Tone : IIR first-order lowpass</p></li>
<li><p>ButLP : IIR second-order lowpass (Butterworth)</p></li>
<li><p>MoogLP : IIR fourth-order lowpass (+ resonance as an extra parameter)</p></li>
</ul>
<p>Complementary highpass filters for the Tone and ButLP objects are Atone
and ButHP. Another common highpass filter is the DCBlock object, which
can be used to remove DC component from an audio signal.</p>
<p>The next example will present bandpass filters.</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"># Three different lowpass filters</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.Tone" title="pyo.lib.filters.Tone"><span class="n">tone</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.Tone" title="pyo.lib.filters.Tone"><span class="n">Tone</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>
<a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.ButLP" title="pyo.lib.filters.ButLP"><span class="n">butlp</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.ButLP" title="pyo.lib.filters.ButLP"><span class="n">ButLP</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>
<a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.MoogLP" title="pyo.lib.filters.MoogLP"><span class="n">mooglp</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.MoogLP" title="pyo.lib.filters.MoogLP"><span class="n">MoogLP</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="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.Tone" title="pyo.lib.filters.Tone"><span class="n">tone</span></a><span class="p">,</span> <a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.ButLP" title="pyo.lib.filters.ButLP"><span class="n">butlp</span></a><span class="p">,</span> <a class="sphinx-codeautolink-a" href="../../api/classes/filters.html#pyo.MoogLP" title="pyo.lib.filters.MoogLP"><span class="n">mooglp</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=Tone, 1=ButLP, 2=MoogLP)"</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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