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
Richter-tuned harmonica note downwards in pitch. This allows for every note on the XB-40 to be bent downwards a whole-tone or more, whereas on standard diatonics only certain notes (the higher-pitched in the cell) will bend at all. The other Richter-tuned harmonica of this kind is the Suzuki SUB30 Ultrabend. Where the XB-40 uses valves and a total of 40 reeds, the SUB30 takes a different approach. Each hole of the harmonica houses a third reed, totalling thirty reeds altogether and thus, where the harmonica draws its name. The third reed is dubbed a "sympathetic reed", tuned one tone below the pitch