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<refentry id="fof">
<indexterm id="IndexFof"><primary>fof</primary></indexterm>
<refentryinfo><title>Signal Generators:Granular Synthesis</title></refentryinfo>
<refmeta>
<refentrytitle>fof</refentrytitle>
</refmeta>
<refnamediv>
<refname>fof</refname>
<refpurpose>
Produces sinusoid bursts useful for formant and granular synthesis.
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<para>
Audio output is a succession of sinusoid bursts initiated at frequency <emphasis>xfund</emphasis> with a spectral peak at <emphasis>xform</emphasis>. For <emphasis>xfund</emphasis> above 25 Hz these bursts produce a speech-like formant with spectral characteristics determined by the k-input parameters. For lower fundamentals this generator provides a special form of granular synthesis.
</para>
</refsect1>
<refsect1>
<title>Syntax</title>
<synopsis>ares <command>fof</command> xamp, xfund, xform, koct, kband, kris, kdur, kdec, iolaps, \
ifna, ifnb, itotdur [, iphs] [, ifmode] [, iskip]</synopsis>
</refsect1>
<refsect1>
<title>Initialization</title>
<para>
<emphasis>iolaps</emphasis> -- number of preallocated spaces needed to hold overlapping burst data. Overlaps are frequency dependent, and the space required depends on the maximum value of <emphasis>xfund * kdur</emphasis>. Can be over-estimated at no computation cost. Uses less than 50 bytes of memory per <emphasis>iolap</emphasis>.
</para>
<para>
<emphasis>ifna, ifnb</emphasis> -- table numbers of two stored functions. The first is a sine table for sineburst synthesis (size of at least 4096 recommended). The second is a rise shape, used forwards and backwards to shape the sineburst rise and decay; this may be linear (<link linkend="GEN07"><citetitle>GEN07</citetitle></link>) or perhaps a sigmoid (<link linkend="GEN19"><citetitle>GEN19</citetitle></link>).
</para>
<para>
<emphasis>itotdur</emphasis> -- total time during which this <emphasis>fof</emphasis> will be active. Normally set to p3. No new sineburst is created if it cannot complete its <emphasis>kdur</emphasis> within the remaining <emphasis>itotdur</emphasis>.
</para>
<para>
<emphasis>iphs</emphasis> (optional, default=0) -- initial phase of the fundamental, expressed as a fraction of a cycle (0 to 1). The default value is 0.
</para>
<para>
<emphasis>ifmode</emphasis> (optional, default=0) -- formant frequency mode. If zero, each sineburst keeps the <emphasis>xform</emphasis> frequency it was launched with. If non-zero, each is influenced by <emphasis>xform</emphasis> continuously. The default value is 0.
</para>
<para>
<emphasis>iskip</emphasis> (optional, default=0) -- If non-zero, skip initialisation (allows legato use).
</para>
</refsect1>
<refsect1>
<title>Performance</title>
<para>
<emphasis>xamp</emphasis> -- peak amplitude of each sineburst, observed at the true end of its rise pattern. The rise may exceed this value given a large bandwidth (say, Q < 10) and/or when the bursts are overlapping.
</para>
<para>
<emphasis>xfund</emphasis> -- the fundamental frequency (in Hertz) of the impulses that create new sinebursts.
</para>
<para>
<emphasis>xform</emphasis> -- the formant frequency, i.e. freq of the sinusoid burst induced by each <emphasis>xfund</emphasis> impulse. This frequency can be fixed for each burst or can vary continuously (see <emphasis>ifmode</emphasis>).
</para>
<para>
<emphasis>koct</emphasis> -- octaviation index, normally zero. If greater than zero, lowers the effective <emphasis>xfund</emphasis> frequency by attenuating odd-numbered sinebursts. Whole numbers are full octaves, fractions transitional.
</para>
<para>
<emphasis>kband</emphasis> -- the formant bandwidth (at -6dB), expressed in Hz. The bandwidth determines the rate of exponential decay throughout the sineburst, before the enveloping described below is applied.
</para>
<para>
<emphasis>kris, kdur, kdec</emphasis> -- rise, overall duration, and decay times (in seconds) of the sinusoid burst. These values apply an enveloped duration to each burst, in similar fashion to a Csound <emphasis>linen</emphasis> generator but with rise and decay shapes derived from the <emphasis>ifnb</emphasis> input. <emphasis>kris</emphasis> inversely determines the skirtwidth (at -40 dB) of the induced formant region. <emphasis>kdur</emphasis> affects the density of sineburst overlaps, and thus the speed of computation. Typical values for vocal imitation are .003,.02,.007.
</para>
<para>
Csound's <emphasis>fof</emphasis> generator is loosely based on Michael Clarke's C-coding of IRCAM's <emphasis>CHANT</emphasis> program (Xavier Rodet et al.). Each fof produces a single formant, and the output of four or more of these can be summed to produce a rich vocal imitation. <emphasis>fof</emphasis> synthesis is a special form of granular synthesis, and this implementation aids transformation between vocal imitation and granular textures. Computation speed depends on <emphasis>kdur, xfund</emphasis>, and the density of any overlaps.
</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
Here is an example of the fof opcode. It uses the file <ulink url="examples/fof.csd"><citetitle>fof.csd</citetitle></ulink>.
<example>
<title>Example of the fof opcode.</title>
<para>See the sections <link linkend="UsingRealTime"><citetitle>Real-time Audio</citetitle></link> and <link linkend="CommandFlags"><citetitle>Command Line Flags</citetitle></link> for more information on using command line flags.</para>
<xi:include href="examples-xml/fof.csd.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
</example>
The formant values for the alto-"a" sound were taken from the <link linkend="MiscFormants"><citetitle>Formant Values Appendix</citetitle></link>.
</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<link linkend="fof2"><citetitle>fof2</citetitle></link>,
<link linkend="MiscFormants"><citetitle>Formant Values Appendix</citetitle></link>
</para>
</refsect1>
<refsect1>
<title>Credits</title>
<para>Added in version 1 (1990)</para>
</refsect1>
</refentry>
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