FORTUNE — Twitter TWTR has called off talks to buy SoundCloud, the German music-streaming service, according to The Wall Street Journal.

The paper has also reported that Twitter allowed a deadline for exclusivity on talks to pass because “the numbers didn’t add up.” If the purchase had gone through, it would have been the largest for the social media service yet.

SoundCloud is a free site that lets users upload and share audio files.

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In October, Twitter purchased MoPub, a mobile ad network, for $350 million. SoundCloud, meanwhile, is valued at $750 million.

“We don’t comment on rumor and speculation,” wrote a Twitter spokesperson in response to a request for comment. A spokesperson for SoundCloud said the company has “no comment” on the state of the deal.