Early in his career, West pioneered a style of hip-hop production dubbed "chipmunk-soul." His method of sampling technique is reminiscent of record production from the 1990s, involving the manipulation of tempo in order to chop and stretch pitched-up samples from vintage soul songs. According to mixing engineer Craig Bauer, the co-owner of Hinge Studios, a downtown Chicago recording and mixing facility where West has been a client, "He knew what he wanted, and he was always striving to make his beats sound like no one else's. He would lift samples and manipulate them—twist them around, turn them up an octave—until he got something fresh out of something that was made twenty or thirty years ago. He never wanted to be like someone else." This is typically done on an Akai MPC or an Ensoniq ASR-10 and combined with his own instrumentation. West further developed his style on his debut studio album, "The College Dropout" (2004). On the album, West formed the constitutive elements of his style: intricate hip-hop beats, topical subject matter, and clumsy rapping laced with inventive wordplay. After a rough version was leaked, West meticulously refined the production, adding string arrangements, gospel choirs, and improved drum programming. Alongside soul samples, the record was characterized by its relatable lyrics. West drew from his own experiences after leaving college to pursue music and recovering from a near-fatal car accident. The record saw West diverge from the then-dominant gangster persona in hip hop in favor of more diverse, topical lyrical subjects. His songs found him rapping about higher education, materialism, self-consciousness, minimum-wage labor, institutional prejudice, class struggle, family, sexuality, and his own self-doubts and personal struggles in the music industry in a manner particular to his middle-class upbringing.