On the following two instances where The Pixies perform on David Letterman, Paul Shaffer inserts his keyboard beats.  Paul Shaffer adds something that doesn't need to be added and frankly annoys me to hear added.  No Shaffer, The Pixies are doing just fine without your hokey sound, no need to mess up their performances.  That's right, he does this not only in 1992, but also in 2004.