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<h2>
<span class="refentrytitle">follow2</span>
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<p>follow2 —
Another controllable envelope extractor.
</p>
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<div class="refsect1" title="Description">
<a id="id2913493"></a>
<h2>Description</h2>
<p>
A controllable envelope extractor using the algorithm attributed to Jean-Marc Jot.
</p>
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<div class="refsect1" title="Syntax">
<a id="id2913507"></a>
<h2>Syntax</h2>
<pre class="synopsis">ares <span class="command"><strong>follow2</strong></span> asig, katt, krel</pre>
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<div class="refsect1" title="Performance">
<a id="id2913525"></a>
<h2>Performance</h2>
<p>
<span class="emphasis"><em>asig</em></span> -- the input signal whose envelope is followed
</p>
<p>
<span class="emphasis"><em>katt</em></span> -- the attack rate (60dB attack time in seconds)
</p>
<p>
<span class="emphasis"><em>krel</em></span> -- the decay rate (60dB decay time in seconds)
</p>
<p>
The output tracks the amplitude envelope of the input signal. The rate at which the output grows to follow the signal is controlled by the <span class="emphasis"><em>katt</em></span>, and the rate at which it decreases in response to a lower amplitude, is controlled by the <span class="emphasis"><em>krel</em></span>. This gives a smoother envelope than <span class="emphasis"><em>follow</em></span>.
</p>
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<div class="refsect1" title="Examples">
<a id="id2914474"></a>
<h2>Examples</h2>
<p>
Here is an example of the follow2 opcode. It uses the file <a class="ulink" href="examples/follow2.csd" target="_top"><em class="citetitle">follow2.csd</em></a>, and <a class="ulink" href="examples/beats.wav" target="_top"><em class="citetitle">beats.wav</em></a>.
</p>
<div class="example">
<a id="id2914497"></a>
<p class="title">
<b>Example 259. Example of the follow2 opcode.</b>
</p>
<div class="example-contents">
<p>See the sections <a class="link" href="UsingRealTime.html" title="Real-Time Audio"><em class="citetitle">Real-time Audio</em></a> and <a class="link" href="CommandFlags.html" title="Csound command line"><em class="citetitle">Command Line Flags</em></a> for more information on using command line flags.</p>
<pre class="programlisting">
<span class="csdtag"><CsoundSynthesizer></span>
<span class="csdtag"><CsOptions></span>
<span class="comment">; Select audio/midi flags here according to platform</span>
<span class="comment">; Audio out Audio in No messages</span>
-odac -iadc -d <span class="comment">;;;RT audio I/O</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o follow2.wav -W ;;; for file output any platform</span>
<span class="csdtag"></CsOptions></span>
<span class="csdtag"><CsInstruments></span>
<span class="comment">; Initialize the global variables.</span>
<span class="ohdr">sr</span> <span class="op">=</span> 44100
<span class="ohdr">kr</span> <span class="op">=</span> 4410
<span class="ohdr">ksmps</span> <span class="op">=</span> 10
<span class="ohdr">nchnls</span> <span class="op">=</span> 1
<span class="comment">; Instrument #1 - play a WAV file.</span>
<span class="oblock">instr</span> 1
a1 <span class="opc">soundin</span> "beats.wav"
<span class="opc">out</span> a1
<span class="oblock">endin</span>
<span class="comment">; Instrument #2 - have another waveform follow the WAV file.</span>
<span class="oblock">instr</span> 2
<span class="comment">; Follow the WAV file.</span>
as <span class="opc">soundin</span> "beats.wav"
af <span class="opc">follow2</span> as, 0.01, 0.1
<span class="comment">; Use a noise waveform.</span>
ar <span class="opc">rand</span> 44100
<span class="comment">; Have it use the amplitude of the followed WAV file.</span>
a1 <span class="opc">balance</span> ar, af
<span class="opc">out</span> a1
<span class="oblock">endin</span>
<span class="csdtag"></CsInstruments></span>
<span class="csdtag"><CsScore></span>
<span class="comment">; Play Instrument #1 for two seconds.</span>
<span class="stamnt">i</span> 1 0 2
<span class="comment">; Play Instrument #2 for two seconds.</span>
<span class="stamnt">i</span> 2 2 2
<span class="stamnt">e</span>
<span class="csdtag"></CsScore></span>
<span class="csdtag"></CsoundSynthesizer></span>
</pre>
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<p><br class="example-break" />
</p>
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<div class="refsect1" title="Credits">
<a id="id2914535"></a>
<h2>Credits</h2>
<p>
</p>
<table border="0" summary="Simple list" class="simplelist">
<tr>
<td>Author: John ffitch</td>
</tr>
<tr>
<td>The algorithm for the <span class="emphasis"><em>follow2</em></span> is attributed to Jean-Marc Jot.</td>
</tr>
<tr>
<td>University of Bath, Codemist Ltd.</td>
</tr>
<tr>
<td>Bath, UK</td>
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<tr>
<td>February 2000</td>
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</table>
<p>
</p>
<p>Example written by Kevin Conder.</p>
<p>New in Csound version 4.03</p>
<p>Added notes by Rasmus Ekman on September 2002.</p>
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