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<section id="table-lookup-py-table-as-transfer-function">
<h1>08-table-lookup.py - Table as transfer function.<a class="headerlink" href="#table-lookup-py-table-as-transfer-function" title="Permalink to this heading">¶</a></h1>
<p>In computer science, a lookup table is an array that replaces runtime computation
with a simpler array indexing operation. The savings in terms of processing time
can be significant, since retrieving a value from memory is often faster than
undergoing an “expensive” computation.</p>
<p>This technic is also used a lot in audio synthesis, where the waveform can be
pre-computed and stored in a table, then simply readed with a ramp at the desired
frequency.</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>
<a class="sphinx-codeautolink-a" href="../../api/classes/players.html#pyo.SfPlayer" title="pyo.lib.players.SfPlayer"><span class="n">src</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/flute.aif"</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"># Arctangent transfer function table.</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/tables.html#pyo.AtanTable" title="pyo.lib.tables.AtanTable"><span class="n">table</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/tables.html#pyo.AtanTable" title="pyo.lib.tables.AtanTable"><span class="n">AtanTable</span></a><span class="p">(</span><span class="n">slope</span><span class="o">=</span><span class="mf">0.5</span><span class="p">,</span> <span class="n">size</span><span class="o">=</span><span class="mi">512</span><span class="p">)</span>
<span class="n">table</span><span class="o">.</span><span class="n">view</span><span class="p">()</span>
<span class="c1"># A signal to dynamically control the drive of the transfer function.</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/controls.html#pyo.Sig" title="pyo.lib._core.Sig"><span class="n">drive</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="mf">0.5</span><span class="p">)</span>
<span class="c1"># We give it True to the dataonly argument when opening the sliders window,</span>
<span class="c1"># otherwise the table would be rewrite way too often.</span>
<span class="n">drive</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">0</span><span class="p">,</span> <span class="mi">1</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="mf">0.5</span><span class="p">,</span> <span class="n">dataOnly</span><span class="o">=</span><span class="kc">True</span><span class="p">)],</span> <span class="n">title</span><span class="o">=</span><span class="s2">"Transfer fonction slope"</span><span class="p">)</span>
<span class="c1"># Lookup reads a table given an audio index lying between -1 and 1.</span>
<span class="c1"># It is especially designed to scan a transfer function with an audio signal.</span>
<span class="n">look</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/tableprocess.html#pyo.Lookup" title="pyo.lib.tableprocess.Lookup"><span class="n">Lookup</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/tables.html#pyo.AtanTable" title="pyo.lib.tables.AtanTable"><span class="n">table</span></a><span class="p">,</span> <span class="n">index</span><span class="o">=</span><a class="sphinx-codeautolink-a" href="../../api/classes/players.html#pyo.SfPlayer" title="pyo.lib.players.SfPlayer"><span class="n">src</span></a><span class="p">,</span> <span class="n">mul</span><span class="o">=</span><span class="mf">0.5</span><span class="p">)</span><span class="o">.</span><span class="n">out</span><span class="p">()</span>
<span class="c1"># Function called to redraw the transfer function.</span>
<span class="k">def</span> <span class="nf">redraw</span><span class="p">():</span>
<span class="n">table</span><span class="o">.</span><span class="n">slope</span> <span class="o">=</span> <span class="n">drive</span><span class="o">.</span><span class="n">get</span><span class="p">()</span>
<span class="c1"># We call the "redraw" function every time the "drive" value changes.</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/triggers.html#pyo.TrigFunc" title="pyo.lib.triggers.TrigFunc"><span class="n">trig</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/triggers.html#pyo.TrigFunc" title="pyo.lib.triggers.TrigFunc"><span class="n">TrigFunc</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/triggers.html#pyo.Change" title="pyo.lib.triggers.Change"><span class="n">Change</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">drive</span></a><span class="p">),</span> <span class="n">function</span><span class="o">=</span><span class="n">redraw</span><span class="p">)</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><span class="n">look</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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