On double bass it refers to the technique that is a more vigorous version of pizzicato, where the string is plucked so hard that when released it bounces off the finger board, making a distinctive sound. A percussive sound can also made by smacking the strings with some or all of the fingers on the right hand in between the notes of a bassline, usually in time with the snare drum.
The earliest players of this technique in American music include Steve Brown,[1] Bill Johnson, Pops Foster,[1] Wellman Braud, and Chester Zardis.
Slapping the bass is a technique used by many bands since at least the 1920s; it came into popular use in the 1940s. Slap bass provides a strong downbeat when the string is plucked and a strong back beat when it slaps back onto the fingerboard of the bass. It creates a very percussive sound and adds a lot of drive that is particularly good for dance music.[2]
Yet another explanation is that snapping the strings against the wood of the instrument supplies a crisp, intense sound which can supply the foundation of a dance band.[1] Slap bass was used by Western Swing and Hillbilly Boogie musicians, and became an important component of an early form of rock and roll that combined blues and what was then called hillbilly music—a musical style now referred to as rockabilly. The technique inspired the George and Ira Gershwin song "Slap That Bass".
Jimbo Wallace from the Reverend Horton Heat band is an accomplished slap bass performer.
Slap bass continues to be used in the 21st century, as it is widely used by modern rockabilly and psychobilly band bassists, including Kim Nekroman (Nekromantix), Geoff Kresge (Tiger Army), Scott Owen (The Living End) and Jimbo Wallace (The Reverend Horton Heat). Kresge's rapid slapping ability is all the more remarkable given that for much of his career he was an electric bassist. The top rockabilly and psychobilly bassists have developed the ability to perform rapid triplet slaps at the same time as they play a walking bassline. This video shows German rockabilly bassist Didi Beck performing a virtuosic slapping technique.