Carnatic Music has evolved from ancient Hindu traditions. It was relatively unaffected by the Arabic and Iranian influences that have characterized the Hindustani music of northern India since the late twelfth and early thirteenth centuries as a result of the Islamic conquest of the north In contrast to northern styles, Carnatic music is more thoroughly oriented to the voice. Even when instruments are used alone, they are played somewhat in imitation of singing, generally within a vocal range, and with embellishments that are characteristic of vocal music. Fewer instruments are used in Carnatic than in northern Indian music, and there are no exclusively instrumental forms. The basic principles of raga (melody type, or framework for improvisation) and tala (cyclical rhythmic pattern) are the same in the south and north, but each musical tradition has its own repertoire of actual ragas and talas, and there are many stylistic differences as well. Carnatic music, with its more homogeneous Indian tradition, has evolved far more orderly and uniform systems for the classification of ragas and talas. The chief centres in India for present-day Carnatic music include Tamil Nadu, Karnataka, Andhra Pradesh, and Kerala.