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<div class="refentry" title="pconvolve">
<a id="pconvolve"></a>
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<a id="IndexPconvolve" class="indexterm"></a>
<div class="refnamediv">
<h2>
<span class="refentrytitle">pconvolve</span>
</h2>
<p>convolve —
Convolution based on a uniformly partitioned overlap-save algorithm
</p>
</div>
<div class="refsect1" title="Description">
<a id="id3092843"></a>
<h2>Description</h2>
<p>
Convolution based on a uniformly partitioned overlap-save algorithm. Compared to the <a class="link" href="convolve.html" title="convolve"><em class="citetitle">convolve</em></a> opcode, <span class="emphasis"><em>pconvolve</em></span> has these benefits:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>small delay</p>
</li>
<li class="listitem">
<p>possible to run in real-time for shorter impulse files</p>
</li>
<li class="listitem">
<p>no pre-process analysis pass</p>
</li>
<li class="listitem">
<p>can often render faster than <span class="emphasis"><em>convolve</em></span></p>
</li>
</ul>
</div>
</div>
<div class="refsect1" title="Syntax">
<a id="id3092937"></a>
<h2>Syntax</h2>
<pre class="synopsis">ar1 [, ar2] [, ar3] [, ar4] <span class="command"><strong>pconvolve</strong></span> ain, ifilcod [, ipartitionsize, ichannel]</pre>
</div>
<div class="refsect1" title="Initialization">
<a id="id3092957"></a>
<h2>Initialization</h2>
<p>
<span class="emphasis"><em>ifilcod</em></span>
-- integer or character-string denoting an impulse response soundfile. Multichannel files are supported, the file must have the same sample-rate as the orc. [Note: <span class="emphasis"><em>cvanal</em></span> files cannot be used!] Keep in mind that longer files require more calculation time [and probably larger partition sizes and more latency]. At current processor speeds, files longer than a few seconds may not render in real-time.
</p>
<p>
<span class="emphasis"><em>ipartitionsize</em></span>
(optional, defaults to the output buffersize [-b]) -- the size in samples of each partition of the impulse file. This is the parameter that needs tweaking for best performance depending on the impulse file size. Generally, a small size means smaller latency but more computation time. If you specify a value that is not a power-of-2 the opcode will find the next power-of-2 greater and use that as the actual partition size.
</p>
<p>
<span class="emphasis"><em>ichannel</em></span>
(optional) -- which channel to use from the impulse response data
file.
</p>
</div>
<div class="refsect1" title="Performance">
<a id="id3093936"></a>
<h2>Performance</h2>
<p>
<span class="emphasis"><em>ain</em></span> -- input audio signal.
</p>
<p>
The overall latency of the opcode can be calculated as such [assuming <span class="emphasis"><em>ipartitionsize</em></span> is a power of 2]
</p>
<pre class="programlisting">
ilatency = (ksmps < ipartitionsize ? ipartitionsize + ksmps : ipartitionsize)/sr</pre>
</div>
<div class="refsect1" title="Examples">
<a id="id3093968"></a>
<h2>Examples</h2>
<p>
Instrument 1 shows an example of real-time convolution.
</p>
<p>
Instrument 2 shows how to do file-based convolution with a 'look ahead' method to remove all delay.
</p>
<div class="note" title="NOTE" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Note: NOTE">
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<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Note]" src="images/note.png" />
</td>
<th align="left">NOTE</th>
</tr>
<tr>
<td align="left" valign="top">
<p>
You will need to download the impulse response files from noisevault.com
or replace the filenames with your own impulse files
</p>
</td>
</tr>
</table>
</div>
<div class="informalexample">
<pre class="programlisting">
<span class="ohdr">sr</span> <span class="op">=</span> 44100
<span class="ohdr">ksmps</span> <span class="op">=</span> 100
<span class="ohdr">nchnls</span> <span class="op">=</span> 2
<span class="oblock">instr 1</span>
kmix <span class="op">=</span> .5 <span class="comment">; Wet/dry mix. Vary as desired.</span>
kvol <span class="op">=</span> .5<span class="op">*</span>kmix <span class="comment">; Overall volume level of reverb. May need to adjust</span>
<span class="comment">; when wet/dry mix is changed, to avoid clipping.</span>
<span class="comment">; do some safety checking to make sure we the parameters a good</span>
kmix <span class="op">=</span> (kmix <span class="op"><</span> 0 <span class="op">||</span> kmix <span class="op">></span> 1 <span class="op">?</span> .5 <span class="op">:</span> kmix)
kvol <span class="op">=</span> (kvol <span class="op"><</span> 0 <span class="op">?</span> 0 <span class="op">:</span> .5<span class="op">*</span>kvol<span class="op">*</span>kmix)
<span class="comment">; size of each convolution partion -- for best performance, this parameter needs to be tweaked</span>
ipartitionsize <span class="op">=</span> p4
<span class="comment">; calculate latency of pconvolve opcode</span>
idel <span class="op">=</span> (ksmps <span class="op"><</span> ipartitionsize <span class="op">?</span> ipartitionsize <span class="op">+</span> ksmps <span class="op">:</span> ipartitionsize)<span class="op">/</span><span class="ohdr">sr</span>
<span class="opc">prints</span> "Convolving with a latency of %f seconds%n", idel
<span class="comment">; actual processing</span>
al, ar <span class="opc">ins</span>
awetl, awetr <span class="opc">pconvolve</span> kvol<span class="op">*</span>(al<span class="op">+</span>ar), "Mercedes-van.wav", ipartitionsize
<span class="comment">; Delay dry signal, to align it with the convoled sig</span>
adryl <span class="opc">delay</span> (1<span class="op">-</span>kmix)<span class="op">*</span>al, idel
adryr <span class="opc">delay</span> (1<span class="op">-</span>kmix)<span class="op">*</span>ar, idel
<span class="opc">outs</span> adryl<span class="op">+</span>awetl, adryr<span class="op">+</span>awetr
<span class="oblock">endin</span>
<span class="oblock">instr 2</span>
imix <span class="op">=</span> 0.5 <span class="comment">; Wet/dry mix. Vary as desired.</span>
ivol <span class="op">=</span> .5<span class="op">*</span>imix <span class="comment">; Overall volume level of reverb. May need to adjust</span>
<span class="comment">; when wet/dry mix is changed, to avoid clipping.</span>
ipartitionsize <span class="op">=</span> 32768 <span class="comment">; size of each convolution partion</span>
idel <span class="op">=</span> (ksmps <span class="op"><</span> ipartitionsize <span class="op">?</span> ipartitionsize <span class="op">+</span> ksmps <span class="op">:</span> ipartitionsize)<span class="op">/</span><span class="ohdr">sr</span> <span class="comment">; latency of pconvolve opcode</span>
kcount <span class="opc">init</span> idel<span class="op">*</span><span class="ohdr">kr</span>
<span class="comment">; since we are using a soundin [instead of ins] we can</span>
<span class="comment">; do a kind of "look ahead" by looping during one k-pass</span>
<span class="comment">; without output, creating zero-latency</span>
<span class="olabel">loop</span>:
al, ar <span class="opc">soundin</span> "John_Cage_1.aif", 0
awetl, awetr <span class="opc">pconvolve</span> ivol<span class="op">*</span>(al<span class="op">+</span>ar),"FactoryHall.aif", ipartitionsize
adryl <span class="opc">delay</span> (1<span class="op">-</span>imix)<span class="op">*</span>al,idel <span class="comment">; Delay dry signal, to align it with</span>
adryr <span class="opc">delay</span> (1<span class="op">-</span>imix)<span class="op">*</span>ar,idel
kcount <span class="op">=</span> kcount <span class="op">-</span> 1
<span class="opc">if</span> kcount <span class="op">></span> 0 <span class="opc">kgoto</span> <span class="olabel">loop</span>
<span class="opc">outs</span> awetl<span class="op">+</span>adryl, awetr<span class="op">+</span>adryr
<span class="oblock">endin</span></pre>
</div>
</div>
<div class="refsect1" title="See also">
<a id="id3094570"></a>
<h2>See also</h2>
<p>
<a class="link" href="convolve.html" title="convolve"><em class="citetitle">convolve</em></a>, <a class="link" href="dconv.html" title="dconv"><em class="citetitle">dconv</em></a>.
</p>
</div>
<div class="refsect1" title="Credits">
<a id="id3094596"></a>
<h2>Credits</h2>
<p>
</p>
<table border="0" summary="Simple list" class="simplelist">
<tr>
<td>Author: Matt Ingalls</td>
</tr>
<tr>
<td>2004</td>
</tr>
</table>
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</p>
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