Which pioneering recommendation technique did Spotify first implement that revolutionized music discovery before evolving to their current AI system?

Music streaming services have transformed how we discover and consume music, with recommendation algorithms playing a crucial role in this evolution. These sophisticated systems analyze listening habits, preferences, and even contextual factors to suggest new artists and songs. Behind the scenes, these platforms employ various technical approaches that have reshaped the music industry's promotional and distribution strategies. Test your knowledge of how these powerful recommendation engines work!

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Collaborative Filtering through 'Discover Weekly' playlists
Neural network analysis of audio waveforms called 'BeatSense'
Social graph analysis via 'FriendTracks' system
Mood-based categorization through 'EmotionPlay' algorithm