Aaliyah had a vocal range of a soprano. With the release of her first single "Back & Forth", Dimitri Ehrlich of "Entertainment Weekly" expressed that Aaliyah's "silky vocals are more agile than those of self-proclaimed queen of hip-hop soul Mary J. Blige." Aaliyah described her sound as "street but sweet", which featured her "gentle" vocals over a "hard" beat. Though Aaliyah did not write any of her own material, her lyrics were described as in-depth. She incorporated R&B, pop and hip hop into her music. Her songs were often uptempo and melancholy, revolving around "matters of the heart". Her songs have been said to have "crisp production" and "staccato arrangements" that "extend genre boundaries" while containing "old-school" soul music. When she experimented with other genres, such as Latin pop and heavy metal, critics did not like the attempt. As her albums progressed, writers felt that Aaliyah acted more older, calling her progress a "declaration of strength and independence". Stephen Thomas Erlewine of Allmusic described her eponymous album, "Aaliyah", as "a statement of maturity and a stunning artistic leap forward" and called it one of the strongest urban soul records of its time. She portrayed "unfamiliar sounds, styles and emotions", but managed to please critics with the contemporary sound it contained. Ernest Hardy of "Rolling Stone" felt that Aaliyah reflected a stronger technique, where she gave her best vocal performance. Others felt that she was "satisfying rather than extraordinary", stating that she added little to modern R&B.