The earliest rock guitar solos, as exemplified by popular recordings of Duane Eddy and Link Wray in the late 1950s, were relatively simple instrumental melodies. In the early 1960s, instrumental surf music represented a step forward in the sonic complexity of rock guitar melodies. In 1963, the dramatic, technically advanced electric guitar solo rose to the fore with Lonnie Mack's hit records, "Memphis" and "Wham!" (later covered by The Ventures, Stevie Ray Vaughan and others), and soon, with the advent of blues rock and psychedelic rock in the mid-late 1960s, became a characteristic part of rock music. Later still, guitar solos became a defining feature of the rock genre of heavy metal, in which most songs feature a solo. Metal solos often showcase the virtuosity of the guitarists, especially in metal styles that use shred guitar techniques for rapid playing of scales and arpeggios. Since the 1960s, electric guitarists have often altered the timbre of their guitar adding electronic guitar effects such as reverb, distortion, delay, and chorus to make the sound fuller and add harmonic overtones. Other effects used in solos include the wah pedal and the talk box.