Scordatura
Scordatura (; literally, Italian for "discord", or "mistuning") is a tuning of a string instrument that is different from the normal, standard tuning. It typically attempts to allow special effects or unusual chords or timbre, or to make certain passages easier to play. It is common to notate the finger position as if played in regular tuning, while the actual pitch resulting is altered (scordatura notation). When all the strings are tuned by the same interval up or down, as in the case of the viola in Mozart's "Sinfonia Concertante for Violin, Viola and Orchestra", the part is transposed  as a whole. Bowed string instruments. The invention of scordatura tuning has been attributed to Thomas Baltzar, a prodigious German violinist and composer who is known to have used the technique in around the 1660s, at least a decade before Biber composed his "Rosary Sonatas" in which he employed the tuning technique. Of course, German violinist Hans Hake (1628 – after 1667) includes three works in "Vorstimmung" ("upset tuning") for two violins (#25, #29, & #33) in his collection "Ander Theil Newer Pavanen,…" (Stade: Elias Holwein, 1654) making this attribution false. Scordatura was much used by composers for viola d'amore, violin and  cello, including J. S. Bach, Biber, Vivaldi, Ariosti, Vilsmayr, and others in compositions for violin during the early 18th century. A special type of notation was used to make it easier to read. This notation was also used to notate music for the viola d'amore, an instrument played and composed for by composers such as Biber and Vivaldi. The viola d'amore used a great number of different tunings and writing music for it in scordatura notation was a natural choice for composers of the time. Notable usage of "scordatura" in Western art music. Double bass. The double bass is sometimes  required to play notes lower than the E to which its lowest string is normally tuned. This can be accomplished with a special mechanical extension with which some double basses are equipped or the composer may ask the double bass to tune down its E string, as in, for example, the third movement of Brahms's Requiem, in which Brahms has some of the double basses tune the E-string down to D in order to sustain the low D pedal point or in the 9th Movement of "Ma mère l'oye" (Cinquième tableau – Laideronnette, impératrice des Pagodes), in which Ravel  has the double basses lower their E-strings a semitone. (George Crumb's "A Haunted Landscape" requires that two bassists use C extensions and still tune down past them to B.) Other kinds of scordatura occur most commonly in solo double bass literature, especially including one that raises all four strings a whole step to F'-B'-E-A. Guitar. Alternate tunings other than symmetrically stepped-down versions of standard or drop-D tuning (where the lowest string is tuned down two half-steps for simple barred power or fifth chords) are rare in modern classical guitar music, but before the nineteenth  century they occurred more often. Drop-D tuning remains common. The sixteenth-century guitar typically had four courses (rather than six strings, as the modern classical does), and the seventeenth-century and eighteenth-century guitar typically had five courses. These were subject to a variety of tunings, such that there is some difficulty establishing which, if any, to consider the standard tuning from which the others deviate. It is sometimes suggested that classical guitarists wishing to read Renaissance lute or vihuela tablature tune their guitar E-A-d-f-b-e' since these instruments in this period usually have the  major third between the 3rd and 4th strings. With the exception of bands using seven-, eight- or recently nine-string guitars to extend the instrument's range downwards, rhythm guitar for modern metal almost universally uses stepped-down versions of standard or drop D tuning, with professionals and amateurs alike commonly using terminology like “tuning to C” (same pattern as standard tuning, but all strings lowered by four half-steps) or “Drop C tuning” (drop-D tuning lowered two half-steps). Conversely, other tuning patterns are rare, with the few popular acts using them commonly widely recognized for the fact  (prominent examples being the bands Sonic Youth and Soundgarden). In certain kinds of folk music alternate tunings for guitar can be fairly frequently found, most typically open tunings where the open strings are tuned to a full major, minor, suspended or extended chord. Piano. Relative to other stringed instruments, piano scordatura tuning is very rare, considering the relative difficulty of tuning and re-tuning a piano from equal temperament. However, some 20th and 21st century music calls for certain notes on the piano to be tuned differently, or the entire piano to be tuned altogether.