                           Forest Fire 1.0
                          by  Nathan Sheldon
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    A patch for the Roland JV-1080, JV-2080, XP-50, XP-60 and XP-80.
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Overview:

I heard about a fire patch recently and decided to give it a try myself.  This patch is the result, and it is a fairly good simulation of a large fire, or should I say conflagration.  I call it Forest Fire because it sounds much more like a large fire than whay you may hear in a fire place.  It took a great deal of time to figure out how to create the "poping" and "snapping" sounds commonly heard in a fire.  But the results are passable as a fire.

Requirements:

None (other than a JV or XP synth).  No expansion boards are required.

Control:

Use this:            to do this:
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Modulation           increase the frequency of pops and snaps and
                       slightly increase fire volume.


More Specifics:

This patch uses four TONEs.  The first two use structure 3 and are probably the most interesting to examine of the 4 in hte patch.  I will first explain the premise which this works and then describe some specifics of its settings.

The idea behind the first set of TONEs is to create a poping and snapping sound as may be heard in a wood (or other) fire.  I knew I needed at least short, random pulses that WIDELY varied in frequency and, ideally, varied somewhat in pulse width.  It took me a while, but I finally came up with the sollution of using a booster to "clip" the waveform.  The next delima was what waveform to put through the booster.  After expiramenting with various combinations of the Applause (INT-B 124) waveform and a number of low frequency waveforms in the INT-B bank (from 183 to 192), I found that, with the correct wave gain, Tone Level, and Booster Level on each of the two TONEs, a very nice short pulse with slightly varying pulse widths and widely varied frequency between the pulses was attainable with Low Pulse 2 (INT-B 187).  A key ingrediant was the use of a random LFO applied to the Low Pulse 2 wave (in TONE 2) affecting the pitch so as to vary the frequency between each pulse (and the width of those pulses).  Because the Booster level is set so high (+18 dB), the great majority of the Applause wave (which is summed with the Low Pulse 2 wave) is clipped off (creating silence).  Only the highest peaks (and lowest valleys, depending on the Low Pulse 2 wave's status) of the Applause waveform are not entirely clipped off and are thus heard as short "pops" and "snaps."  After I finally figured this technique out, the rest was fairly simple; a matter of filtering out the low frequency portions of the pops with a High-Pass Filter and randomly modulating that cutoff frequency with a random LFO (so you hear both low- and high-pitched pops).

The other two tones are virtually identical save the small difference in Coarse Tune settings and panning positions.  These TONEs are independant of each other (i.e. Tone Structure 1) and use the Applause waveform dropped nearly three octaves.  Heavy use is made of random LFOs to vary the pan position and levels of each of these two TONEs.  A Band-Pass Filter (BPF) with a little resonance (to make it sound less like fuzz and more like crackles) is used to filter out the loud lower frequencies and unnatural upper harmonics.

Notes And Commnets:

Please feel free to comment on this patch.  You can use it freely
anywhere you wish and re-distribute it (along with this document)
anywhere.  It is, howver, Copyright 1998 by Nathan Sheldon.  :-)  If you
use it in any production that includes credits, please include my name
under synth programming.  I can be reached via e-mail at

nsheldon@geocities.com


Version History:

1.0  Initial release.
