Spotify has responded to user complaints that its shuffle playlists do not actually play songs in random order. Users accused the company of playing songs which generate more revenue more frequently than other tunes.

Users of Spotify have complained that they see patterns in which certain songs are played more often, while others are hardly played at all. The members accused the company of choosing songs for which it receives additional revenue from record companies to promote, while other tunes not on its promotion list are relegated to less frequent plays. Others claimed the company chooses to play those songs for which it has to pay less in royalties

Spotify has vehemently denied the allegations, claiming that the effect is a result of an inaccurate sense of what is random on the part of Spotify users. Users, according to the company, feel that songs from different artists or genres should be spaced apart from each other, as opposed to being played in bunches or close to one another. Spotify claims user's brains recognize patterns that do not actually exist.

"If you just heard a song from a particular artist, that doesn't mean that the next song will be more likely from a different artist in a perfectly random order," Spotify employee Lukáš Poláček posted on the company's blog. "The problem is that, to humans, truly random does not feel random, so we got tons of complaints from users about it not being random," Mattias Johansson, a Spotify software engineer, explained on Quora. "Last year, we updated it with a new algorithm that is intended to feel more random to a human."

The new algorithm ironically makes the order of songs less random for it to feel more random to listeners. It deliberately spaces apart songs from different artists or genres so that they are not played in clumps or bunches, even though true randomness could potentially generate such clumps.

Apple's Steve Jobs received similar complaints and changed the company's algorithm on its iTunes shuffle feature to also space apart songs by the same artist. Still, users of the services still complain.

"Working at Spotify has taught me a few things, one of them being is that it's really, really, really hard to build something that a human will genuinely feel is shuffled." Johansson says. "People still constantly come up to me at parties and tell me that the shuffle functionality is not random." In actuality, since Spotify changed its algorithm, the people are now in fact correct.