Detuner
Detuners are mechanical devices used to simplify the
They can be fitted at either or both ends of any or all of the strings. For example, a relatively common arrangement on the bass guitar is to use a detuner on the lowest string to allow the bassist to switch between 'standard tuning' (E A D G) and 'drop D' (D A D G). The latter provides two extra notes (D and D# / Eb) that are particularly useful in several common keys.
However, there are many possible variants – for example, bass guitarist Michael Manring has made extensive use of detuners in some of his compositions and has a four-stringed bass guitar with multiple detuners. Bass guitarist and youtuber Charles Berthoud also makes extensive use of detuners, generally on a LeFay D-Tuner (which as the name hints was designed with a detuner on each string). Adrian Legg is a popular guitarist making use of rapid tuning changes. He was prominent in the late 1980s.
The idea may have originated from the double bass extenders.