Tuning
The standard tuning of the viol is in fourths, with a major third in the middle (like the standard Renaissance lute tuning). For bass viols, the notes would be (from the lowest) D-G-C-E-A-D, with an additional low A for seven-string bass viols. For the tenor viol, the tuning is G-C-F-A-D-G (a smaller tenor, or "alto" viol, is usually tuned A-D-G-B-E-A). The treble viol is one octave higher than the bass.
Alternate tunings (called scordatura) were often employed, particularly in the solo lyra viol style of playing, which also made use of many techniques such as chords and pizzicato, not generally used in consort playing. An unusual style of pizzicato was known as a thump. Lyra viol music was also commonly written in tablature. There is a vast repertoire of this music, some by well-known composers and much by anonymous ones.
Much viol music predates the adoption of equal temperament tuning by musicians. The movable nature of the tied-on frets permits the viol player to make adjustments to the tempering of the instrument, and some players and consorts adopt meantone temperaments, which are arguably more suited to Renaissance music. Several fretting schemes involve frets that are spaced unevenly to produce "better-sounding" chords in a limited number of keys. In some of these schemes, the two strands of gut that form the fret are separated so that the player can finger a slightly sharper or flatter version of a note (for example G sharp vs. A flat) to suit different circumstances.
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