Low pass filtering

Can anyone tell me how to filter out everything except the low end of a sample (bass guitar) on the 4000? I've went through the forum and bible however didn't have any luck. I am not the most skilled at filtering, I just play around with it until eye get the desired effect on my D32xd..in addition can someone drop the science behind it filtering in general as my way is quite time consuming. The Reference manuel shows the different types of filters and thats about it.

this should give you an idea
http://www.youtube.com/watch?v=-qArfWFTqf4

Preciate it bro,..i don't know why i didn't start my search on you tube..But i was leaning more towards the various types of low end algorithms sine,6-Pole,4-Pole etc. I've been manipulating the frequences alot better i suppose it's all by ear calibration, but what do the various R/L coordinate frequences and reference stand for on the 4000 in filter mode. I'm alot further in my understanding than I was before, good look