By the end of the decade, Black people were part of the psychedelia and early heavy metal trends, particularly by way of the ubiquitous Beatles' influence and the electric guitar innovations of Jimi Hendrix. Hendrix was among the first guitarists to use audio feedback, fuzz, and other effects pedals such as the wah wah pedal to create a unique guitar solo sound. Psychedelic soul, a mix of psychedelic rock and soul began to flourish with the 1960s culture. Even more popular among Black people, and with more crossover appeal, was album-oriented soul in the late 1960s and early 1970s, which revolutionized African-American music. The genre's intelligent and introspective lyrics, often with a socially aware tone, were created by artists such as Marvin Gaye in "What's Going On", and Stevie Wonder in "Songs in the Key of Life".