As the best known Indian musician, Shankar has helped expand the traditionally closed repertoire of North Indian Classical music. Under the guidance of guru Allauddin Khan, father of Ali Akbar Khan, Shankar forged a split from the more traditional styles of the equally important playing school led by Vilayat Khan. Shankar's initial innovation was a buzzier tone and flashier playing techniques that clashed with the sitar's historically more serious, solemn tone, drawing criticism from more conservative musicians. Collaborations with Western Artists such as Yehudi Menuhin and The Beatles further opened the music's boundaries, paving the way for more experimental outings by artists including Zakir Hussain and Trilok Gurtu. Though his sound became synonymous with psychedelia in the '60s, Shankar did not enjoy the role of "trip" leader. Indeed, it takes a very clear mind and vigorous practice to reach the level of technical mastery and spiritual power that Shankar has achieved.