String instrument strings, or play them by rolling the bell of a brass instrument such as a trombone on the array of strings. However, these are relatively rarely used special techniques. Other keyed string instruments, small enough for a strolling musician to play, include the plucked autoharp, the bowed nyckelharpa, and the hurdy-gurdy, which is played by cranking a rosined wheel. Steel-stringed instruments (such as the guitar, bass, violin, etc.) can be played using a magnetic field. An E-Bow is a small hand-held battery-powered device that magnetically excites the strings of an electric string instrument to provide a sustained, singing tone reminiscent
Hurdy-gurdy intonation and sound quality, each string of a hurdy-gurdy must be wrapped with cotton or similar fibers. The cotton on melody strings tends to be quite light, while drone strings have heavier cotton. Improper cottoning results in a raspy tone, especially at higher pitches. In addition, individual strings (in particular the melody strings) often have to have their height above the wheel surface adjusted by having small pieces of paper placed between the strings and the bridge, a process called "shimming". Shimming and cottoning are connected processes since either one can affect the geometry of the instrument's strings. In some