London, May 6 (IANS): Contrary to popular belief, the so-called "British Invasion" of US pop music by groups like The Beatles and The Rolling Stones did not start rock revolution, researchers have found.

The greatest musical revolution in US pop history was also not 1964 but 1991 when hip-hop arrived in the charts, said the team that studied trends in style, the diversity of the charts, and the timing of musical revolutions in last 50 years.

They found that 1986 was the least diverse year for the charts, a fact the researchers attribute to the sudden popularisation of drum machines and samplers at the time.

"For the first time, we can measure musical properties in recordings on a large scale. We can actually go beyond what music experts tell us by looking directly into the songs, measuring their makeup and understanding how they have changed," said Matthias Mauch from Queen Mary University of London.

The team noticed that the musical revolution said to have been driven by The Beatles and The Rolling Stones was already underway before they arrived in the US.

"The rise of hip-hop caused the single most radical change in the US charts," Mauch added.

For the study, Mauch and researchers from Imperial College London, with the help from music website Last.fm, used cutting edge methods from signal processing and text-mining to analyse the musical properties of songs.

They analysed 17,000 songs from the US Billboard Hot 100 charts from 1960 to 2010.

Their system automatically grouped the thousands of songs by patterns of chord changes and tone allowing researchers to statistically identify trends with an unprecedented degree of consistency.

"No doubt some will disagree with our scientific approach and think it's too limited for such an emotional subject but I think we can add to the wonder of music by learning more about it," Mauch said.

"We want to analyse more music from more periods in more countries and build a comprehensive picture of how music evolves," the authors concluded.

The findings were detailed in the journal Royal Society Open Science.