When playing slap bass a common misconception is that you are restricted to a simple slap and pop melody, many bassists constrict themselves by not realizing they are able to use more than just their index finger when playing a slap groove. Here is a clear example of how the second finger (and in later lessons even the third) can be used in their basic form to pop when playing a slap and pop riff. Let’s start off with the double popping then, Shall we?
The basic concept:
S = Slap.
H = Hammer-On.
P = Pull-Off
P(1) = Pop (With first finger).
P(2) = Pop (with second finger).
G|------------7------------------x-----------7---------9---------------
D|---------------------------------------------------------------------
A|---------------------------------------------------------------------
E|--0------------------0---------------------------------------0-------
S P (1) S P (1) P (2) S
There's a little bit of improvisation in this but here's a brief video I made. The Fundamental Riff itself is there and you can hear how it is achieved. What I would like to stress is that this isn't a technique that is usually picked up very quickly if you've never tried it before but with time and a great many blisters on your middle finger it can be successfully achieved and prove very handy in your soloing. So what we have here is the basic repetitive riff using the double-pop technique which we can build off quite easily using the E pentatonic.
For example:
H
G|------------7------------------x-----------7---------9---------------
D|---------------------------------------------------------------------
A|---------------------------------------------------------------------
E|--0------------------0---------------------------------------x-------
S P (1) S P (1) P (2) S
H
G|----x--------------------x---------------------x---------7-------9---
D|---------------------------------------------------------------------
A|---------------------------------------------------------------------
E|--------------0----------------------0-------------------------------
P (1) S P (2) S P (1) P (2)
H H H P H P
G|--------------7----------7-------------------------------------------
D|---7----9-----------9----------9-----7/5----7----5-------------------
A|-------------------------------------------------------7-------------
E|---------------------------------------------------------------------
S S S S
H
G|---------------x--------7---------9----------------------------------
D|---------------------------------------------------------------------
A|---------------------------------------------------------------------
E|----x----------------------------------------------------------------
S P (1) P (2)
As a technique there are probably better examples than this from far better Bassists than I of how to use the technique to the best of it's potential, but looking at the groove in that first bar as a technique, that can not be done with one popping finger and it creates a very definitive sound in comparison.
/ my profile 
