Which groundbreaking recommendation technology did Spotify acquire in 2014 to dramatically improve its music personalization system?

Before streaming dominated the music industry, retail was the primary way people purchased music. Spotify revolutionized music consumption with its innovative recommendation algorithm that transformed how listeners discover new artists and songs. Test your knowledge about this game-changing retail innovation that disrupted traditional music sales channels and created a new paradigm for music consumption and discovery.

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The Echo Nest
Shazam's AudioID
SoundHound's Houndify
Pandora's Music Genome Project