I've heard people talk about playing ahead and behind the beat and I've never been sure what this really means or why you would do it. If you're playing behind the beat, does that mean that you hit everything you would normally hit a fraction of a second later than you would if you were playing it in perfect time with the metronome? Or do you just play the snare hit a fraction of a second later, and keep everything else (bass drum, etc) in perfect time?
To me it seems like this would be really hard to do without a metronome to help guide you, since you naturally want to try to stay on the beat. Could someone give me an example of either of these techniques being used in a song? or some pointers on how to develop this skill and what the advantages of it would be? I'd really appreciate it.
Playing "behind the beat" can mean a few different things. In the first Elvin Jones example, the drummer is also "bending" the time, blurring the distinction between straight and swung. Occasionally some downbeats are late, but he catches up. Two different things going on here, often in the same measure, in this "lazy" playing.
To play behind the beat as a drummer requires the presence of a metronome, or a musician who wants to play slightly ahead of you (a rare bird indeed!). In most traditions, the band plays on, or slightly behind the drums, so the drums take an on-center approach. A horn section will play behind the drummer as well, more so if they're unfamiliar with their material!
A rock guitarist might play ahead of the drums, but may also prefer to play on-center (think Green Day).
Another way to play behind the beat is to stretch the distance between beat 1 and beat 2 a bit (and I mean just a tiny bit!). A great example is P-Funk's Up For The Downstroke! All four quarter notes are not created equal! Weird, but man does it work! It makes the 1 feel so much heavier! I don't think P-Funk was sober enough to know what they were doing, btw.
To learn to play behind the beat, get out your metronome and play quarters with one hand on the hi-hat. Allow yourself to get behind, but stay behind only slightly, so that the click and your hit create a flam. Now rush a bit and catch up to the click, then drag a bit and get behind again. Repeat this process with your left hand, then bass drum, and then finally with a simple beat.
Repeat the above exercise, but this time rush a bit and get ahead of the click, then drag and return to being on-center, and so on.
To really feel who is playing behind the beat takes quite a bit of experience. My band right now has a bass player who is on-center, or ahead, of the beat. He's a good player, but it's frustrating, and it doesn't sound right.
About "pocket":
In gospel circles, playing "in the pocket" usually means playing good time, keeping the beat steady, and with the appropriate feel (straight, swung, etc.). But "playing pocket" usually means playing without much embellishment or fills.