What’s a really simple explanation of vamping? Thanks.
Vamping is a rhythmic style of picking while chording. The chords typically are closed (that is, all 4 fretting strings fretted). The banjo plays either boom/chick (downbeat/offbeat), or when an instrument like bass or guitar is providing the “boom”, it might just do the “chick” (offbeat).
Either of these is called vamping. When doing the “boom”, the thumb usually hits the 4th string alone. The other, chording part includes a slight relaxing of the chording fingers, to quickly deaden the strings right after they sound their tones very briefly. The strong sound being quickly muted leaves a lot of space to hear what’s being accompanied, while still providing a good rhythmic groove for the singer or soloing player to follow. To mute the strings, all that’s needed is a slight relaxation of the grip, so the strings naturally lift off the frets. When touching the left fingers only, the strings are muted.
For examples of me using this technique, you can see it easily on my Bluegrass Jamming DVD. When playing along, you can just copy me and I’m sure you’ll get the hang of it. It’s a very common and useful backup technique, one that should be used by banjoists more often, as a roll can sometimes “step on” a soloing instrument, and can wear out a listener when heard constantly, even in the background.