As far as I can ascertain it is about a simulation which defines electric guitar pickups.
The title is:
Approximating the Electric Guitar Pickup
 

It's more like an examination of a LCR filter.

Mike, this is the Art Tube Pre...
http://artproaudio.com/art_products/signal_processing/signal_channel_tube_preamps/product/tube_mp-original/
 Input Impedance XLR, l/4”2K ohms, 840K ohms
 
Cactus, my Seagull has the same LR Baggs system.
 

840k. Good.
 
The next step is to find out what the output impedance is for the particular LR Baggs system that you have.
 
It's probably something like 840ohm.
 
If the ratio between output and input is greater than 1:5 or 1:10 you can probably discount a concern about impedance loading altering the tonality of the signal.
 
As an example 840:840,000 is a 1:1000 ratio. The 470k input on the UCX represents something like a 1:500 ratio.
 
You might want to look to the innards of the preamp circuit for reasons why the different patches sound different, or you might just want to remember which patch you like better and roll with it.
 
Have fun!!!
 
best regards,
mike