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<H2>
fog</H2>
<PRE> ar <B>fog</B> xamp, xdens, xtrans, xspd, koct, kband, kris, \
kdur, kdec, iolaps, ifna, ifnb, itotdur[, iphs] \
[, itmode]</PRE>
<HR>
<H4>
<U>DESCRIPTION</U></H4>
Audio output is a succession of grains derived from data in a stored function
table <I>ifna</I>. The local envelope of these grains and their timing
is based on the model of <A HREF="fof.html">fof</A> synthesis and permits
detailed control of the granular synthesis.
<H4>
<U>INITIALIZATION</U></H4>
<I>iolaps</I> - number of pre-located spaces needed to hold overlapping
grain data. Overlaps are density dependent, and the space required depends
on the maximum value of <I>xdens</I>* <I>kdur</I>. Can be over-estimated
at no computation cost. Uses less than 50 bytes of memory per <I>iolaps</I>.
<P><I>ifna</I>, <I>ifnb</I> - table numbers of two stored functions. The
first is the data used for granulation, usually from a soundfile (GEN01).
The second is a rise shape, used forwards and backwards to shape the grain
rise and decay; this is normally a sigmoid (GEN19) but may be linear (GEN07).
<P><I>itotdur</I> - total time during which this <B>fog</B> will be active.
Normally set to p3. No new grain is created if it cannot complete its <I>kdur</I>
within the remaining <I>itotdur</I>.
<P><I>iphs</I> (optional) - initial phase of the fundamental, expressed
as a fraction of a cycle (0 to 1). The default value is 0.
<P><I>itmode</I> (optional) - transposition mode. If zero, each grain keeps
the <I>xtrans</I> value it was launched with. if non-zero, each is influenced
by <I>xtrans</I> continuously. The default value is 0.
<H4>
<U>PERFORMANCE</U></H4>
<I>xamp</I> - amplitude factor. Amplitude is also dependent on the number
of overlapping grains, the interaction of the rise shape (<I>ifnb</I>)
and the exponential decay (<I>kband</I>), and the scaling of the grain
waveform (<I>ifna</I>). The actual amplitude may therefore exceed <I>xamp</I>.
<P><I>xdens</I> - density. The frequency of grains per second.
<P><I>xtrans</I> - transposition factor. The rate at which data from the
stored function table <I>ifna</I> is read within each grain. This has the
effect of transposing the original material. A value of 1 produces the
original pitch. Higher values transpose upwards, lower values downwards.
Negative values result in the function table being read backwards.
<P><I>xspd</I> - speed. The rate at which successive grains advance through
the stored function table <I>ifna</I>. <I>xspd</I> is in the form of an
index (0 to 1) to <I>ifna</I>. This determines the movement of a pointer
used as the starting point for reading data within each grain. (<I>xtrans</I>
determines the rate at which data is read starting from this pointer.)
<P><I>koct</I> - octaviation index. The operation of this parameter is
identical to that in fof.
<P><I>kband</I>, <I>kris</I>, <I>kdur</I>, <I>kdec</I> - grain envelope
shape. These parameters determine the exponential decay (<I>kband</I>),
and the rise (<I>kris</I>), overall duration (<I>kdur</I>,) and decay (<I>kdec</I>
) times of the grain envelope. Their operation is identical to that of
the local envelope parameters in fof.
<P>The Csound <B>fog</B> generator is by Michael Clarke, extending his
earlier work based on IRCAM's fof algorithm.
<H4>
<U>EXAMPLE:</U></H4>
<PRE> ;p4 = transposition factor
;p5 = speed factor
;p6 = function table for grain data
i1 = sr/ftlen(p6) ;scaling to reflect sample rate and table length
a1 <B>phasor</B> i1*p5 ;index for speed
a2 <B>fog</B> 5000, 100, p4, a1, 0, 0, , .01, .02, .01, 2, p6, 1, p3, 0, 1</PRE>
<H4>
<U>AUTHOR:</U></H4>
Michael Clark
<BR>Huddersfield
<BR>May 1997
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