Anyway, bass guitar is a somewhat unusual instrument in music. It's both a rhythm and a melodic instrument, so it has to hold down the rhythm while supporting the rest of the instruments. While there are some musicians who seem to favor melody over rhythm and others who tend to focus on maintaining the rhythmic structure, both are essential for good grooving basslines. The ones who can do both are rightly fully considered to be masters of the instrument.

One of the things that I really appreciate about good drummers is how well they are able to hold down the meter. When a bass player has a solid drummer supporting the rhythms, it frees him up from having to do all the maintenance that is required to keep the rest of the band in time. Now, that doesn't mean that the bass player can just wander off into space, playing notes in whatever tempo happens to pop into his pretty little head, but a strong drummer can build out a tight pocket. And then the bass line can sit just a bit behind the beat or ahead of it, and that breathes depth into the music.

And here's a little observation that I have made over the years. Good drummers understand time, meter and rhythm. Great drummers understand that drums are not only a rhythm instrument, that they are melodic as well. From something simple as tuning the toms to minor 3rds for a darker sound to choosing an array of cymbals and using their different tonalities to color the sound (as opposed to hitting the whichever cymbal happens to be most convenient to the drummer's hand at the time), the drummers that I go out of my way to play with are the ones that have rock solid time and approach their instrument as more than just backbeats.

When the drummer is locked on to the tempo, she and the bass player can start to work together. Her pattern on the kick drum will set up the rhythmic choices for his bass line. He can double up the same pattern (which will bring a lot emphasis to the bass line and groove — check out this one hit wonder from the 80's for an example), build on top of the pattern (accenting the doubled notes while growing the feel — the examples are too numerous to mention, but here's one anyway), he can play against it (doing a counterpoint to add complexity to the overall song — the rhythmic intricacy of this song beggars the belief to start with: that Jamerson played the entire line with one finger while lying down on this back is just astounding) or the bass player can do a combination of these three techniques at the same time. The typical bass line tends to heavily favor the first two approaches, while almost all bass lines utilize all three combinations at one time or another.