Twitter is reportedly setting its sights on an acquisition of SoundCloud -- the music sharing service being called the "YouTube for audio." SoundCloud, which was launched in 2007, announced it reached 250 million monthly active users last October. The social audio service allows users to upload audio that others can stream or download for free. Users can also follow each other, which can help lesser-known artists gain a following and big name artists generate buzz. The service announced a $60 million funding round earlier this year that valued the company at $700 million. The most Twitter has paid in an acquisition was more than $300 million for MoPub last year.