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<p>follow —
Envelope follower unit generator.
</p>
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<div class="refsect1" title="Description">
<a id="idp24018000"></a>
<h2>Description</h2>
<p>
Envelope follower unit generator.
</p>
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<div class="refsect1" title="Syntax">
<a id="idp24059824"></a>
<h2>Syntax</h2>
<pre class="synopsis">ares <span class="command"><strong>follow</strong></span> asig, idt</pre>
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<div class="refsect1" title="Initialization">
<a id="idp24060912"></a>
<h2>Initialization</h2>
<p>
<span class="emphasis"><em>idt</em></span> -- This is the period, in seconds, that the average amplitude of <span class="emphasis"><em>asig</em></span> is reported. If the frequency of <span class="emphasis"><em>asig</em></span> is low then <span class="emphasis"><em>idt</em></span> must be large (more than half the period of <span class="emphasis"><em>asig</em></span> )
</p>
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<div class="refsect1" title="Performance">
<a id="idp24062776"></a>
<h2>Performance</h2>
<p>
<span class="emphasis"><em>asig</em></span> -- This is the signal from which to extract the envelope.
</p>
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<div class="refsect1" title="Examples">
<a id="idp24063728"></a>
<h2>Examples</h2>
<p>
Here is an example of the follow opcode. It uses the file <a class="ulink" href="examples/follow.csd" target="_top"><em class="citetitle">follow.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="idp24065136"></a>
<p class="title">
<strong>Example 286. Example of the follow opcode.</strong>
</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>
-odac <span class="comment">;;;realtime audio out</span>
<span class="comment">;-iadc ;;;uncomment -iadc if realtime audio input is needed too</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o follow.wav -W ;;; for file output any platform</span>
<span class="csdtag"></CsOptions></span>
<span class="csdtag"><CsInstruments></span>
<span class="ohdr">sr</span> <span class="op">=</span> 44100
<span class="ohdr">ksmps</span> <span class="op">=</span> 32
<span class="ohdr">nchnls</span> <span class="op">=</span> 2
<span class="ohdr">0dbfs</span> <span class="op">=</span> 1
<span class="oblock">instr</span> 1
asig <span class="opc">soundin</span> "beats.wav"
<span class="opc">outs</span> asig, asig
<span class="oblock">endin</span>
<span class="oblock">instr</span> 2 <span class="comment">;envelope follower</span>
as <span class="opc">soundin</span> "beats.wav"
as <span class="op">=</span> as<span class="op">*</span>.7 <span class="comment">;reduce volume a bit</span>
at <span class="opc">tone</span> as, 500 <span class="comment">;smooth estimated envelope</span>
af <span class="opc">follow</span> at, p4
asin <span class="opc">poscil3</span> .5, 440, 1
<span class="comment">; "beats.wav" provides amplitude for poscil</span>
asig <span class="opc">balance</span> asin, af
<span class="opc">outs</span> asig, asig
<span class="oblock">endin</span>
<span class="csdtag"></CsInstruments></span>
<span class="csdtag"><CsScore></span>
<span class="comment">;sine wave.</span>
<span class="stamnt">f</span> 1 0 32768 10 1
<span class="stamnt">i</span> 1 0 2
<span class="stamnt">i</span> 2 2 2 0.001 <span class="comment">;follow quickly</span>
<span class="stamnt">i</span> 2 5 3 0.2 <span class="comment">;follow slowly</span>
<span class="stamnt">e</span>
<span class="csdtag"></CsScore></span>
<span class="csdtag"></CsoundSynthesizer></span>
</pre>
</div>
</div>
<p><br class="example-break" />
</p>
<p>
To avoid zipper noise, by discontinuities produced from complex envelope tracking, a lowpass filter could be used, to smooth the estimated envelope.
</p>
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<div class="refsect1" title="Credits">
<a id="idp24067944"></a>
<h2>Credits</h2>
<p>
</p>
<table border="0" summary="Simple list" class="simplelist">
<tr>
<td>Author: Paris Smaragdis</td>
</tr>
<tr>
<td>MIT, Cambridge</td>
</tr>
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<td>1995</td>
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