Which machine learning approach revolutionized Spotify's recommendation system in 2015, dramatically improving personalized playlist creation like 'Discover Weekly'?

Streaming platforms have transformed how we discover and consume music, with personalization algorithms creating eerily accurate playlists tailored to our tastes. But how much do you know about the technology powering these recommendations? This trivia question explores the cutting-edge retail personalization algorithms that major music streaming services employ to keep listeners engaged and discovering new artists.

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Neural Word Embedding models that analyze lyrics and music blog text
Collaborative filtering based solely on user listening history
Convolutional neural networks analyzing audio waveforms
Reinforcement learning systems optimizing for listener retention