Bending Vibraphone Pitch Up - April 1, 2012 by BarryK
I always thought that pitch bending the vibraphone was an interesting technique, but I don't really like it. I recently figured out why. It changes the pitch lower. It is a kind of sad sound to me. In contrast, guitarists bend pitch up by stretching the guitar strings. That is a happier sound to me.
To lower the pitch on a vibraphone, you get a hard rubber mallet, press it on the node (at the string), hit the bar with another mallet, then move the hard mallet towards the center of the bar.