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<div class="refentry" title="svfilter">
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<a id="IndexSvfilter" class="indexterm"></a>
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<h2>
<span class="refentrytitle">svfilter</span>
</h2>
<p>svfilter —
A resonant second order filter, with simultaneous lowpass, highpass and bandpass outputs.
</p>
</div>
<div class="refsect1" title="Description">
<a id="idp46830992"></a>
<h2>Description</h2>
<p>
Implementation of a resonant second order filter, with simultaneous lowpass, highpass and bandpass outputs.
</p>
</div>
<div class="refsect1" title="Syntax">
<a id="idp46856840"></a>
<h2>Syntax</h2>
<pre class="synopsis">alow, ahigh, aband <span class="command"><strong>svfilter</strong></span> asig, kcf, kq [, iscl]</pre>
</div>
<div class="refsect1" title="Initialization">
<a id="idp46857968"></a>
<h2>Initialization</h2>
<p>
<span class="emphasis"><em>iscl</em></span> -- coded scaling factor, similar to that in <a class="link" href="reson.html" title="reson"><em class="citetitle">reson</em></a>. A non-zero value signifies a peak response factor of 1, i.e. all frequencies other than <span class="emphasis"><em>kcf</em></span> are attenuated in accordance with the (normalized) response curve. A zero value signifies no scaling of the signal, leaving that to some later adjustment (see <a class="link" href="balance.html" title="balance"><em class="citetitle">balance</em></a>). The default value is 0.
</p>
</div>
<div class="refsect1" title="Performance">
<a id="idp46860304"></a>
<h2>Performance</h2>
<p>
<span class="emphasis"><em>svfilter</em></span> is a second order state-variable filter, with k-rate controls for cutoff frequency and Q. As Q is increased, a resonant peak forms around the cutoff frequency. <span class="emphasis"><em>svfilter</em></span> has simultaneous lowpass, highpass, and bandpass filter outputs; by mixing the outputs together, a variety of frequency responses can be generated. The state-variable filter, or "multimode" filter was a common feature in early analog synthesizers, due to the wide variety of sounds available from the interaction between cutoff, resonance, and output mix ratios. <span class="emphasis"><em>svfilter</em></span> is well suited to the emulation of "analog" sounds, as well as other applications where resonant filters are called for.
</p>
<p>
<span class="emphasis"><em>asig</em></span> -- Input signal to be filtered.
</p>
<p>
<span class="emphasis"><em>kcf</em></span> -- Cutoff or resonant frequency of the filter, measured in Hz.
</p>
<p>
<span class="emphasis"><em>kq</em></span> -- Q of the filter, which is defined (for bandpass filters) as bandwidth/cutoff. <span class="emphasis"><em>kq</em></span> should be in a range between 1 and 500. As <span class="emphasis"><em>kq</em></span> is increased, the resonance of the filter increases, which corresponds to an increase in the magnitude and "sharpness" of the resonant peak. When using <span class="emphasis"><em>svfilter</em></span> without any scaling of the signal (where <span class="emphasis"><em>iscl</em></span> is either absent or 0), the volume of the resonant peak increases as Q increases. For high values of Q, it is recommended that <span class="emphasis"><em>iscl</em></span> be set to a non-zero value, or that an external scaling function such as <a class="link" href="balance.html" title="balance"><em class="citetitle">balance</em></a> is used.
</p>
<p>
<span class="emphasis"><em>svfilter</em></span> is based upon an algorithm in Hal Chamberlin's <span class="emphasis"><em>Musical Applications of Microprocessor</em></span>s (Hayden Books, 1985).
</p>
</div>
<div class="refsect1" title="Examples">
<a id="idp46867456"></a>
<h2>Examples</h2>
<p>
Here is an example of the svfilter opcode. It uses the file <a class="ulink" href="examples/svfilter.csd" target="_top"><em class="citetitle">svfilter.csd</em></a>.
</p>
<div class="example">
<a id="idp46868448"></a>
<p class="title">
<strong>Example 840. Example of the svfilter 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>
<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 svfilter.wav -W ;;; for file output any platform</span>
<span class="csdtag"></CsOptions></span>
<span class="csdtag"><CsInstruments></span>
<span class="comment">; Orchestra file for resonant filter sweep of a sawtooth-like waveform. </span>
<span class="comment">; The seperate outputs of the filter are scaled by values from the score,</span>
<span class="comment">; and are mixed together.</span>
<span class="ohdr">sr</span> <span class="op">=</span> 44100
<span class="ohdr">kr</span> <span class="op">=</span> 2205
<span class="ohdr">ksmps</span> <span class="op">=</span> 20
<span class="ohdr">nchnls</span> <span class="op">=</span> 1
<span class="oblock">instr</span> 1
idur <span class="op">=</span> p3
ifreq <span class="op">=</span> p4
iamp <span class="op">=</span> p5
ilowamp <span class="op">=</span> p6 <span class="comment">; determines amount of lowpass output in signal</span>
ihighamp <span class="op">=</span> p7 <span class="comment">; determines amount of highpass output in signal</span>
ibandamp <span class="op">=</span> p8 <span class="comment">; determines amount of bandpass output in signal</span>
iq <span class="op">=</span> p9 <span class="comment">; value of q</span>
iharms <span class="op">=</span> (<span class="ohdr">sr</span><span class="op">*</span>.4) <span class="op">/</span> ifreq
asig <span class="opc">gbuzz</span> 1, ifreq, iharms, 1, .9, 1 <span class="comment">; Sawtooth-like waveform</span>
kfreq <span class="opc">linseg</span> 1, idur <span class="op">*</span> 0.5, 4000, idur <span class="op">*</span> 0.5, 1 <span class="comment">; Envelope to control filter cutoff</span>
alow, ahigh, aband <span class="opc">svfilter</span> asig, kfreq, iq
aout1 <span class="op">=</span> alow <span class="op">*</span> ilowamp
aout2 <span class="op">=</span> ahigh <span class="op">*</span> ihighamp
aout3 <span class="op">=</span> aband <span class="op">*</span> ibandamp
asum <span class="op">=</span> aout1 <span class="op">+</span> aout2 <span class="op">+</span> aout3
kenv <span class="opc">linseg</span> 0, .1, iamp, idur <span class="op">-</span>.2, iamp, .1, 0 <span class="comment">; Simple amplitude envelope</span>
<span class="opc">out</span> asum <span class="op">*</span> kenv
<span class="oblock">endin</span>
<span class="csdtag"></CsInstruments></span>
<span class="csdtag"><CsScore></span>
<span class="stamnt">f</span>1 0 8192 9 1 1 .25
<span class="stamnt">i</span>1 0 5 100 1000 1 0 0 5 <span class="comment">; lowpass sweep</span>
<span class="stamnt">i</span>1 5 5 200 1000 1 0 0 30 <span class="comment">; lowpass sweep, octave higher, higher q</span>
<span class="stamnt">i</span>1 10 5 100 1000 0 1 0 5 <span class="comment">; highpass sweep</span>
<span class="stamnt">i</span>1 15 5 200 1000 0 1 0 30 <span class="comment">; highpass sweep, octave higher, higher q</span>
<span class="stamnt">i</span>1 20 5 100 1000 0 0 1 5 <span class="comment">; bandpass sweep</span>
<span class="stamnt">i</span>1 25 5 200 1000 0 0 1 30 <span class="comment">; bandpass sweep, octave higher, higher q</span>
<span class="stamnt">i</span>1 30 5 200 2000 .4 .6 0 <span class="comment">; notch sweep - notch formed by combining highpass and lowpass outputs</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>
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<div class="refsect1" title="Credits">
<a id="idp46870760"></a>
<h2>Credits</h2>
<p>
</p>
<table border="0" summary="Simple list" class="simplelist">
<tr>
<td>Author: Sean Costello</td>
</tr>
<tr>
<td>Seattle, Washington</td>
</tr>
<tr>
<td>1999</td>
</tr>
</table>
<p>
</p>
<p>New in Csound version 3.55</p>
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