Mandolin are used. Usually, courses of 2 adjacent strings are tuned in unison. By far the most common tuning is the same as violin tuning, in scientific pitch notation G–D–A–E, or in Helmholtz pitch notation: g–d′–a′–e″. Note that the numbers of Hz shown above assume a 440 Hz A, standard in most parts of the western world. Some players use an A up to 10 Hz above or below a 440, mainly outside the United States. Other tunings exist, including "cross-tunings", in which the usually doubled string runs are tuned to different pitches. Additionally, guitarists may sometimes tune a mandolin to
Dropped A tuning Dropped A tuning Dropped A tuning is an alternate tuning for a 7 string guitar where the lowest string is tuned down ("dropped") from the standard B by one whole step to A as follows A1-E2-A2-D3-G3-B3-E4. Also, for a 6 string guitar, dropped A tuning is achieved by tuning all strings down a 4th with the lowest string tuned 1 additional step down as follows A1-E2-A2-D3-F#3-B3. This is a "drop 1" tuning in the key of B (i.e. tune the whole guitar down a perfect fourth from standard tuning, then tune the 6th string a whole step down). As a