Which pioneering machine learning technique did Spotify introduce in 2015 that revolutionized music recommendations by analyzing raw audio files rather than just user behavior?

In today's digital music landscape, streaming platforms have become sophisticated recommendation engines powered by machine learning. These AI systems analyze billions of listening patterns to personalize your music experience. But how well do you understand the technology behind those eerily accurate song suggestions? Test your knowledge about how machine learning is transforming music discovery, consumption, and marketing in the streaming era.

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Convolutional Neural Networks (CNN) for audio classification
Collaborative Filtering through matrix factorization
Natural Language Processing (NLP) of user reviews
Reinforcement Learning for playlist generation