The Erhu has two strings tuned in d1-a1. First described in Song Dynasty (A.D. 420-479), the Erhu is an ancient instrument which is extremely popular in China today as both traditional and contemporary music. Consisting of a drum-like mahogany sound box covered with a snake skin head, two steel strings stretched from the sound box along a narrow bridge, sound is generated by a horse hair bamboo bow. The Erhu’s musical range spans about four octaves, and while the sound is very similar to a Western violin, it differs by being much more nasal in quality. Because there is no fingerboard against which the player can press, finger pressure is a critical part of Erhu technique. Assuming this aspect of Erhu playing is  mastered, the lack of a finger board actually allows for a tremendous flexibility for the Erhu player in controlling the sound and expressiveness of this instrument - a flexibility approaching that of the human voice. (Description found at "George Gao's Chinese Classical Music Site")