The rapid rise of digital music sales has stalled in the United States, the world’s biggest and most important market, with sales in the first half of 2010 flat compared with a year before. According to research group Nielsen, digital sales were flat in the U.S. market after a 13 percent increase from 2008 to 2009 and 28 percent growth from 2007 to 2008.

Major music companies such as Vivendi’s Universal Music have pinned their hopes on boosting legal digital sales to counter online piracy and the collapse in CD sales.

Jean Littolff, managing director of Nielsen Music, told Reuters the flat U.S. sales could be due to weak consumer confidence, the appeal of new music releases and confusion over the many different ways people can buy music online.

“I think this is a plateau, it doesn’t mean that this digital consumption is going to drop significantly,” he said. “It’s a plateau, but it’s not yet saturation.”

The digital music market has mostly been led by a-la-carte sales on sites such as Apple’s iTunes, with the sale of individual tracks or albums, and Nielsen said subscription streaming services where consumers pay for access to music were still struggling to make an impact in the mass market.

So-called audio-visual streaming sites such as YouTube however continued to be hugely popular, while mobile phone music services were getting more traction.

According to the Nielsen research, digital music sales were up 7 percent in Britain, up 13 percent in Germany and up 19 percent in France.