The Vibrato
The vibrato is what distinguishes a vibraphone from a simple xylophone or marimba.
Inside each resonator tube, a small rotating disc alternates between open and closed positions at approximately 5 to 6 Hz. This creates the undulating "wah-wah" effect characteristic of jazz masters like Lionel Hampton, Milt Jackson, and of course Geo Daly.
Try it yourself: on the home page's interactive vibraphone, click the Vibrato button to toggle the effect.