five-string instrument with a D major tuning in thirds and fourths (F1–A1–D2–F♯2–A2); four-string instruments omit the bottom string. Due to this feature, it does not have a true viol tuning. If a fifth string was present, its tuning could be variable, potentially going as low as D1. It played almost exclusively at 16′, though it was used commonly as a chamber and solo instrument (even from the 17th century) and was the preferred double bass instrument in the Viennese Classical period ( 1760–1820). Some concertos for the bass, e.g., by Wanhal and Dittersdorf, were composed with this tuning in mind. Contrabass or double bass. These terms are again problematic from a historical perspective (often meaning something slightly different from a modern reader might expect), but here refer to three- or four-string instruments that (usually) do not have frets—of all the types of violoni, these are the ones that most closely resemble modern double basses. The strings may be tuned in fourths (E1–A1–D2–G2 like most modern double basses) or in fifths (C1–G1–D2–A2 a full octave lower than the cello), and if there are only 3 strings, the missing string is almost always the lowest one (i.e. A1–D2–G2 or G1–D2–A2). In the 18th and 19th century, many bassists used only three strings, as it was thought that removing a string made the instrument more sonorous and resonant. It may also be tuned in fifths (C1–G1–D2 or G1–D2–A2). Other types In the Renaissance and Baroque era and even in the 2000s, there are players who changed or adapted their instruments in unique ways, for example Ganassi's Regola Rubertina (1542-43). In this category we might find bass viols that are tuned in E (E2-A2-D3-F3-B3-E4) (instead of D), or where the bottom string is tuned an extra step lower, to a C2 (a pitch found in numerous Baroque works). We might find tenor viols that are tuned in F (F2-B2-E3-G3-C4-F4) (instead of G) (called baritone viols). We might find treble viols that are tuned in B (B2-E3-A3-C4-F4-B4) (instead of D) (called haute-contre (high tenor) de violes). Or we might find a contrabass/double bass tuned in fourths, but with a top string a fourth higher than is standard (A1–D2–G2–C3) or another contrabass/double bass tuned in fourths but with its bottom string tuned down to a low C. Looking only at modern Viol de Gamba based instruments, there are five. History Both the violin and viol families