Nielsen has been giving its annual presentation at the NARM conference, revealing the latest trends in digital music. It’s predicted that half of all recorded music unit purchases will be digital by the end of 2010, although in revenue terms, digital won’t overtake physical until 2011.Nielsen also pointed out that just 35% of US album sales in 2008 were from new albums released that year – the lowest such percentage since it started collating sales using SoundScan. Catalogue digital albums were up 37% in 2008, compared to current digital albums rising by 27%. On the individual track front, 40% of all track sales in 2008 were from songs released in 2007 or 2008, with 60% classed as catalogue sales.Nielsen also had bad music for SanDisk”s slotMusic memory-card albums. It claims that 105,000 have been sold through Best Buy and Wal-Mart in the last seven and a half months, but that average weekly sales are down 65% since the start of 2009.