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<h2 class="title"><a id="OrchTop"></a>Syntax of the Orchestra</h2>
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<p>
The Csound orchestra (.orc) or the <span class="emphasis"><em><CsInstruments></em></span> section of a csd file, contains:
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<p>A <a class="link" href="OrchTop.html#OrchHeader" title="Orchestra Header Statements"><em class="citetitle">header section</em></a>, which specifies global options for instrument performance</p>
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<p>A list of <a class="link" href="OrchUDO.html" title="User Defined Opcodes (UDO)"><em class="citetitle">User defined opcodes</em></a> and <a class="link" href="OrchIblock.html" title="Instrument and Opcode Block Statements"><em class="citetitle">instrument blocks</em></a> containing UDO and instrument definitions.</p>
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<p>
The orchestra header, instrument blocks, and UDOs contain <span class="emphasis"><em>Orchestra statements</em></span>. An <span class="emphasis"><em>orchestra statement</em></span> in Csound has the format:
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<pre class="synopsis">
label: <span class="returnvalue">result</span> <code class="function">opcode</code> <em class="parameter"><code>argument1</code></em>, <em class="parameter"><code>argument2</code></em>, <em class="parameter"><code>...</code></em> ;comments
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The label is optional and identifies the basic statement that follows as the potential target of a go-to operation (see <a class="link" href="ControlPgmctl.html" title="Program Flow Control"><em class="citetitle">Program Flow Control</em></a>). A label has no effect on the statement per se.
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Depending on their function, some opcodes produce no output, so they have no result value. Others take no arguments and only produce a result.
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<p>
Every orchestra statement must be on a single line, however long lines can be wrapped to a new line using the '\' character. This character indicates that the next line is part of the current one, this way you can split a line for easier reading, like this:
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<pre class="programlisting">
a2 <span class="opc">oscbnk</span> kcps, 1.0, kfmd1, 0.0, 40, 203, 0.1, 0.2, kamfr, kamfr2, 148, \
0, 0, 0, 0, 0, 0, -1, \
kfnum, 3, 4</pre>
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</p>
<p>
Comments are optional and are for the purpose of letting the user document his orchestra code. Comments begin with a semicolon (;) and extend to the end of the line. Comments can optionally be in C-style, spanning multiple lines like this:
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<pre class="programlisting">
<span class="comment">/* Anything in here --------
is a comment which can span
several lines --------- */</span></pre>
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<p>
The remainder (result, opcode, and arguments) form the basic statement. This also is optional, i.e. a line may have only a label or comment or be entirely blank. If present, the basic statement must be complete on one line, and is terminated by a carriage return and line feed.
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<p>
The opcode determines the operation to be performed; it usually takes some number of input values (or arguments, with a maximum value of about 800); and it usually has a result field variable to which it sends output values at some fixed rate. There are four possible rates:
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<p>once only, at orchestra setup time (effectively a permanent assignment)</p>
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<p>once at the beginning of each note (at initialization (init) time: i-rate)</p>
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<p>once every performance-time control loop (perf-time control rate, or k-rate)</p>
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<p>once each sound sample of every control loop (perf-time audio rate, or a-rate)</p>
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<div class="section" title="Orchestra Header Statements">
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<div>
<h2 class="title" style="clear: both"><a id="OrchHeader"></a>Orchestra Header Statements</h2>
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<p>
The <span class="emphasis"><em>Orchestra Header</em></span> contains global information that applies to all instruments and defines aspects of Csound output. It is sometimes referred to as <span class="emphasis"><em>instr 0</em></span>, because it behaves as an instrument, but without k- or a-rate processing (i.e. only opcodes and instructions that work at i-rate are allowed).
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<p>
An <span class="emphasis"><em>orchestra header statement</em></span> operates once only, at orchestra setup time. It is most commonly an assignment of some value to a <span class="emphasis"><em>global reserved symbol</em></span> , e.g. sr = 20000. All orchestra header statements belong to a pseudo instrument 0, an <span class="emphasis"><em>init</em></span> pass of which is run prior to all other instruments at score time 0. Any <span class="emphasis"><em>ordinary statement</em></span> can serve as an orchestra header statement, eg. gifreq = cpspch(8.09) provided it is an init-time only operation. Statements that are normally placed in an orchestra header are:
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<p>
<a class="link" href="Zerodbfs.html" title="0dbfs">
<em class="citetitle">0dbfs</em>
</a>
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<p>
<a class="link" href="ctrlinit.html" title="ctrlinit">
<em class="citetitle">ctrlinit</em>
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<p>
<a class="link" href="ftgen.html" title="ftgen">
<em class="citetitle">ftgen</em>
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<a class="link" href="kr.html" title="kr">
<em class="citetitle">kr</em>
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<a class="link" href="ksmps.html" title="ksmps">
<em class="citetitle">ksmps</em>
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<a class="link" href="massign.html" title="massign">
<em class="citetitle">massign</em>
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<a class="link" href="nchnls.html" title="nchnls">
<em class="citetitle">nchnls</em>
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<p>
<a class="link" href="pgmassign.html" title="pgmassign">
<em class="citetitle">pgmassign</em>
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<a class="link" href="pset.html" title="pset">
<em class="citetitle">pset</em>
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<a class="link" href="seed.html" title="seed">
<em class="citetitle">seed</em>
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<a class="link" href="sr.html" title="sr">
<em class="citetitle">sr</em>
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<a class="link" href="strset.html" title="strset">
<em class="citetitle">strset</em>
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<p>
For example, a Csound header may look like:
</p>
<pre class="programlisting">
<span class="ohdr">sr</span> = 44100
<span class="ohdr">kr</span> = 4410
<span class="ohdr">ksmps</span> = 10
<span class="ohdr">nchnls</span> = 2
<span class="ohdr">0dbfs</span> = 1
<span class="ohdr">massign</span> 1, 10</pre>
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