Much of Johnson's music featured experimental improvisations that would now be categorized as jazz rather than blues. According to the blues historian Gérard Herzhaft, Johnson was "undeniably the creator of the guitar solo played note by note with a pick, which has become the standard in jazz, blues, country, and rock". Johnson's style reached both the Delta bluesmen and urban players who would adapt and develop his one-string solos into the modern electric blues style. However, the writer Elijah Wald declared that in the 1920s and 1930s Johnson was best known as a sophisticated and urbane singer rather than an instrumentalist: "Of the forty ads for his records that appeared in the "Chicago Defender" between 1926 and 1931, not one even mentioned that he played guitar."