Repeated phrases in music impart the all-important yet undefined "feel" of a song. Percussion instruments often define the beat, repeating clusters of rhythmic phrases, but when it comes to melodic and chording instruments, both the rhythm and notes combine. With these instruments, repeated sections are dubbed vamps or riffs, depending on the musical purpose of the section.
"A riff is a group of notes that forms part of a melodic idea, usually performed at that instant, never to be utilized again in that exact form in that particular space or solo," Canadian saxophonist and music teacher Stan Szymkow says, speaking of the riff in a jazz context. Also called a motif or lick, the riff usually serves as a basis for improvisation and soloing. "A riff can be part of the recognizable melody," says Syzmkow, or it can be its own invention outside of the song.
In rock music, the riff may take on monolithic importance. Music critic Greg Kot, writing for BBC in 2014, says a great rock riff can shape a song by becoming the core of the tune, the hook listeners recall. He cites The Rolling Stones' "(I Can't Get No) Satisfaction," Deep Purple's "Smoke on the Water" and Nirvana's "Smells Like Teen Spirit" as examples of great songs that open with riffs. Unlike jazz, a rock riff tends to be repeated literally, anchoring the song.
Building on the Vamp
"A vamp is a repeating sequence of notes, following a strict harmonic offering," says Szymkow. This provides the harmonic base for a section. Used as a verb, he says, it serves as a type of shorthand for musicians. For example, "vamp on the last four chords of the tune, until the soloist or singer starts" defines a repeating section the rest of the band easily understands. While the musicians may not play each repetition identically, they would be bound by the harmonic structure of those four chords. While it oversimplifies, vamping may be thought of as chord-based, while riffs are melodic.
As well as the riff and the vamp, ostinatos and loops also describe repeated musical sections. The ostinato most often is a classical term. Unlike the vamp, which can be variable, ostinatos are defined in length by the score; but like the vamp, they may progress within the same harmonic structure. Loops are popular in contemporary music and can be assembled as building blocks with computer software. A loop most often is copied and pasted -- repetition built from one section, used again and again.