[PD] help with oscillator modulation

[oliver]

hi, dear list !

here's one for all synth wizards ...

in trying to understand sound synthesis a little better than i do,
i'm attempting to clone a nice VST synth that i like a lot (POLYVOKS).

it's a fairly simple synth and i understand and can recreate most of
it's features and functions, safe for the following:

POLYVOKS has 2 Oscillators. Osc 1 can be modulated by 2 different 
sources:
1.) a global LFO
2.) Oscillator 2

while point 1 is easy, i didn'zt succeed in finding out what's going on
when OSC 1 is "modulated" by OSC 2. it doesn't sound like any of the 
classical
modulation techniques (RM, FM, PM) but more like a 
combination/modification
of the above that i'm not able to figure out. my guess is that the OSC2 
get's
itself "modulated" while it modulates OSC 1 (depending on the mod 
amount)

please, if anybody might want to have a look at the following example 
patch.
it includes the things i tried so far and a 4 second sample of the 
original
(= the modulation effect recorded from the VST synth).

http://klingt.org/fileservice/downloads/00693153753552230-mod_osc_210918.zip

my testing setup was this: the synth got a note (C1) and both 
Oscillators
had the same waveform (sine) and octave offset. then i raised the 
modulation
(OSC2 -> OSC1) from min to max, over a course of 4 seconds.

if anybody has an idea what's going on here, that would be a big help !

thanks a lot in advance

oliver