DSP Robotics Support

Heya,
I'm getting into my guitar sound,
and have been recommended this->
http://www.softube.com/index.php?id=af
I was wondering-
what is the function in FS that does this?
Is it just a scaled add of the out back to in?
Or something more complicated?
Cheers and all success

my guess would be a harmonic of the original note.

Adding the 'original' may be apart of the initial sustaining ... but then the upper harmonics can start sliding in.

Just a drummers guess