GDAE is the standard tuning for the four strings on a violin. With this tuning, the lowest note is the G below middle C, and each string is separated from its neighbors by a perfect fifth. In comparison, the standard tuning for a viola is one fifth lower, at CGDA. Occasionally, non-standard tunings, known as scordatura, are used, especially where certain special effects are desired, such as to produce a mysterious or eerie sound, and in some folk music.