Doo-wop is a genre of rhythm and blues based on vocal harmony, developed in the late 1940s and 1950s in urban African-American communities. It is characterized by multi-part vocal harmonies and 'nonsense' syllables (like 'doo-wop,' 'shoo-be-doo,' or 'rama-lama-ding-dong') used as rhythmic accompaniment. The style originated on street corners and in subway stations because the acoustics of those locations enhanced the natural reverb of the voices. Most doo-wop groups consisted of four or five singers, including a high tenor for the lead and a deep bass for the 'thumping' rhythmic foundation. Because instruments were expensive, the singers used their voices to mimic brass or percussion. Doo-wop influenced the early stages of Rock and Roll and paved the way for the 'girl group' and 'boy band' movements of later decades.