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<section id="multi-rate-processing-py-doing-processing-at-very-high-sampling-rate">
<h1>01-multi-rate-processing.py - Doing processing at very high sampling rate.<a class="headerlink" href="#multi-rate-processing-py-doing-processing-at-very-high-sampling-rate" title="Permalink to this heading">¶</a></h1>
<p>In numerical audio computing, it is sometimes useful to be able to process
a signal with much more timing precision than what the usual sampling rates
offer. A typical case is when the effect applied to the sound adds a lot of
harmonics. Higher harmonics will quickly wrap around the Nyquist frequency,
producing aliasing in the output signal. The solution is to increase the
sampling rate, so the nyquist frequency, and to use anti-aliasing filters
when converting from one rate to another.</p>
<p>Pyo allows to compute chunks of code at different sampling rates than the
one with which the server was started. You should do this only for the objects
you need to process with a higher sampling rate, without changing the server’s
sampling rate, otherwise the program will be very CPU consuming.</p>
<p>You start a new resampling block with the method:</p>
<blockquote>
<div><p>Server.beginResamplingBlock(x)</p>
</div></blockquote>
<p>where <cite>x</cite>, a power-of-two, is the resampling factor. A negative power-of-two
will start a downsampling block of code.</p>
<p>To close the block, simply call:</p>
<blockquote>
<div><p>Server.endResamplingBlock()</p>
</div></blockquote>
<p>Everything between the two calls will be computed with the new sampling rate.</p>
<p>Audio signals must be resampled before used with a different sampling rate.
The Resample object does this. Inside a resampling block, it will convert the
signal to the new sampling rate, and outside the resampling block, it will
convert the signal back to the original sampling rate. Its <cite>mode</cite> argument lets
choose the quality of the interpolation/decimation filter used to resample 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="c1"># We create a new class for our upsampled distortion effect.</span>
<span class="k">class</span> <span class="nc">UpSampDisto</span><span class="p">:</span>
<span class="sd">"""</span>
<span class="sd"> Upsampled distortion effect.</span>
<span class="sd"> :Args:</span>
<span class="sd"> input: PyoObject</span>
<span class="sd"> The signal to process.</span>
<span class="sd"> drive: float or PyoObject, optional</span>
<span class="sd"> Amount of distortion applied to the signal, between 0 and 1.</span>
<span class="sd"> upfactor: int (power-of-two), optional</span>
<span class="sd"> Resampling factor.</span>
<span class="sd"> filtmode: int, optional</span>
<span class="sd"> The interpolation/decimation mode. See Resample's man page</span>
<span class="sd"> for details.</span>
<span class="sd"> """</span>
<span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="nb">input</span><span class="p">,</span> <span class="n">drive</span><span class="o">=</span><span class="mf">0.5</span><span class="p">,</span> <span class="n">upfactor</span><span class="o">=</span><span class="mi">8</span><span class="p">,</span> <span class="n">filtmode</span><span class="o">=</span><span class="mi">32</span><span class="p">):</span>
<span class="c1"># The InputFader object lets change its input signal without clicks.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">input</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/internals.html#pyo.InputFader" title="pyo.lib._core.InputFader"><span class="n">InputFader</span></a><span class="p">(</span><span class="nb">input</span><span class="p">)</span>
<span class="c1"># Convert the drive argument to audio signal.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">drive</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">Sig</span></a><span class="p">(</span><span class="n">drive</span><span class="p">)</span>
<span class="c1"># Get a reference to the audio server.</span>
<span class="n">server</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">drive</span><span class="o">.</span><span class="n">getServer</span><span class="p">()</span>
<span class="c1"># Start an upsampled block of code.</span>
<span class="n">server</span><span class="o">.</span><span class="n">beginResamplingBlock</span><span class="p">(</span><span class="n">upfactor</span><span class="p">)</span>
<span class="c1"># Resample the audio signals. Because the drive signal is only a</span>
<span class="c1"># control signal, a linear interpolation is enough. The input</span>
<span class="c1"># signal uses a much better filter to eliminate aliasing artifacts.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">inputUp</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/utils.html#pyo.Resample" title="pyo.lib.utils.Resample"><span class="n">Resample</span></a><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">input</span><span class="p">,</span> <span class="n">mode</span><span class="o">=</span><span class="n">filtmode</span><span class="p">)</span>
<span class="bp">self</span><span class="o">.</span><span class="n">driveUp</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/utils.html#pyo.Resample" title="pyo.lib.utils.Resample"><span class="n">Resample</span></a><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">drive</span><span class="p">,</span> <span class="n">mode</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span>
<span class="c1"># Apply the distortion effect.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">disto</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/effects.html#pyo.Disto" title="pyo.lib.effects.Disto"><span class="n">Disto</span></a><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">inputUp</span><span class="p">,</span> <span class="n">drive</span><span class="o">=</span><span class="bp">self</span><span class="o">.</span><span class="n">driveUp</span><span class="p">)</span>
<span class="c1"># Close the upsampled block.</span>
<span class="n">server</span><span class="o">.</span><span class="n">endResamplingBlock</span><span class="p">()</span>
<span class="c1"># Convert back the distorted signal to the current sampling rate.</span>
<span class="c1"># Again, we use a good decimination filter to eliminate aliasing.</span>
<span class="bp">self</span><span class="o">.</span><span class="n">output</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/utils.html#pyo.Resample" title="pyo.lib.utils.Resample"><span class="n">Resample</span></a><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">disto</span><span class="p">,</span> <span class="n">mode</span><span class="o">=</span><span class="n">filtmode</span><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="c1"># Define some useful methods.</span>
<span class="k">def</span> <span class="nf">setInput</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">,</span> <span class="n">fadetime</span><span class="o">=</span><span class="mf">0.05</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">input</span><span class="o">.</span><span class="n">setInput</span><span class="p">(</span><span class="n">x</span><span class="p">,</span> <span class="n">fadetime</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">setDrive</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">x</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">drive</span><span class="o">.</span><span class="n">value</span> <span class="o">=</span> <span class="n">x</span>
<span class="k">def</span> <span class="nf">out</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">chnl</span><span class="o">=</span><span class="mi">0</span><span class="p">):</span>
<span class="bp">self</span><span class="o">.</span><span class="n">output</span><span class="o">.</span><span class="n">out</span><span class="p">(</span><span class="n">chnl</span><span class="p">)</span>
<span class="k">return</span> <span class="bp">self</span>
<span class="k">def</span> <span class="nf">sig</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">output</span>
<span class="c1">### Usage example ###</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"># Two different sources for testing, a sine wave and a flute melody.</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/generators.html#pyo.Sine" title="pyo.lib.generators.Sine"><span class="n">src1</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/generators.html#pyo.Sine" title="pyo.lib.generators.Sine"><span class="n">Sine</span></a><span class="p">(</span><span class="n">freq</span><span class="o">=</span><span class="mi">722</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">src1</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.SLMapFreq" title="pyo.lib._maps.SLMapFreq"><span class="n">SLMapFreq</span></a><span class="p">(</span><span class="mi">722</span><span class="p">)],</span> <span class="n">title</span><span class="o">=</span><span class="s2">"Sine frequency"</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">src2</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"># Input source interpolation.</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/utils.html#pyo.Interp" title="pyo.lib.utils.Interp"><span class="n">src</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/utils.html#pyo.Interp" title="pyo.lib.utils.Interp"><span class="n">Interp</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/generators.html#pyo.Sine" title="pyo.lib.generators.Sine"><span class="n">src1</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">src2</span></a><span class="p">,</span> <span class="mi">0</span><span class="p">)</span>
<span class="n">src</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">"interp"</span><span class="p">,</span> <span class="mi">0</span><span class="p">)],</span> <span class="n">title</span><span class="o">=</span><span class="s2">"Source: sine <=> flute"</span><span class="p">)</span>
<span class="c1"># Control for the drive parameter of the distortion.</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/controls.html#pyo.Sig" title="pyo.lib._core.Sig"><span class="n">drv</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">0</span><span class="p">)</span>
<span class="n">drv</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">"Drive"</span><span class="p">)</span>
<span class="c1"># Distortion at current sampling rate.</span>
<a class="sphinx-codeautolink-a" href="../../api/classes/effects.html#pyo.Disto" title="pyo.lib.effects.Disto"><span class="n">dist</span></a> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/effects.html#pyo.Disto" title="pyo.lib.effects.Disto"><span class="n">Disto</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/utils.html#pyo.Interp" title="pyo.lib.utils.Interp"><span class="n">src</span></a><span class="p">,</span> <span class="n">drive</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">drv</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="c1"># Distortion with increased sampling rate.</span>
<span class="n">updist</span> <span class="o">=</span> <span class="n">UpSampDisto</span><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/utils.html#pyo.Interp" title="pyo.lib.utils.Interp"><span class="n">src</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">drv</span></a><span class="p">)</span>
<span class="c1"># Interpolator to compare the two processes.</span>
<span class="n">output</span> <span class="o">=</span> <a class="sphinx-codeautolink-a" href="../../api/classes/utils.html#pyo.Interp" title="pyo.lib.utils.Interp"><span class="n">Interp</span></a><span class="p">(</span><a class="sphinx-codeautolink-a" href="../../api/classes/effects.html#pyo.Disto" title="pyo.lib.effects.Disto"><span class="n">dist</span></a><span class="p">,</span> <span class="n">updist</span><span class="o">.</span><span class="n">sig</span><span class="p">(),</span> <span class="mi">0</span><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="n">output</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">"interp"</span><span class="p">,</span> <span class="mi">0</span><span class="p">)],</span> <span class="n">title</span><span class="o">=</span><span class="s2">"Up Sampling: without <=> with"</span><span class="p">)</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">output</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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