The tapping technique is arguably the most popular of the extended techniques for the guitar. A number of players hailing from different backgrounds perfected variations of the concept throughout the 20th century, though it was definitely brought into the mainstream by Edward Van Halen in the late 70s.
The technique itself consists of fretting the string in the same motion that sets it into vibration. In other words, a single movement is done, 'hammering' the string against the fretboard at a given point, normally with the right hand index or middle fingers. This results in a smooth sounding note, which can be sustained, slided, or more commonly pulled off into any note fretted by the left hand, or an open string. This allows the guitarist to play intervals that would otherwise be impossible to make in a single movement with the left hand only.
This kind of one handed tapping technique, when combined with left hand pull-offs and hammer-ons, can result in a virtually infinite number of patterns that not only give the player the tools to play passages conceived for other instruments, but also, by doing so, pushes the boundaries of the artistic possibilities within the guitar. One of the most common uses is to play extremely fast arpeggiated chord sequences and variations.
As opposed to one handed tapping, which usually employs one or two fingers from the right hand, two handed tapping often employs eight or nine fingers, making it possible to play complex polyphonic textures on the guitar. Guitarists have experimented with different approaches to this, with Emmet Chapman credited as being one of the firsts to use his right hand fingers parallel to the frets. He later developed his own instrument, now called the Chapman Stick, which is almost exclusively played by using two handed tapping. A number of instruments developed on the same principles exist, though the Stick is arguably the most popular one.
Though mostly used by electric guitar players, tapping can be performed on steel-string and nylon-string acoustic instruments also. Modern amplification paved the way for a number of unconventional techniques to be extensively used in acoustic guitars, with tapping being one of them. When used in the electric guitar, tapping can be performed with high levels of overdrive and compression, in order to boost the tapped notes and even out the volumes of the passages.
Some guitarists choose to tap their guitars with picks or other objects, producing particular effects.
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