The singular style of rhythm & blues (R&B) that emerged from New Orleans in the years after World War II played an important role in the development of funk. In a related development, the underlying rhythms of American popular music underwent a basic, yet generally unacknowledged transition from triplet or shuffle feel (12/8) to even or straight eighth notes (8/8). Many jazz historians have shown interest in the process whereby jazz musicians learned to swing (for example, the Fletcher Henderson Orchestra through Louis Armstrong's 1924 arrival in New York), but there has been little analysis of the reverse development – the change back to ‘straighter’ rhythms. The earliest forms of rock 'n' roll, such as the R&B songs that first acquired this label and styles like rockabilly that soon followed, continued to be predominantly in shuffle rhythms. By the 1960s, division of the beat into equal halves had become common practice in the new driving style of rock, and the occurrence of 12/8 metre relatively scarce. Although the move from triplets to even eighths might be seen as a simplification of metre, this shift supported further subdivision to sixteenth-note rhythms that were exploited in New Orleans R&B and funk.