Which machine learning technique was pivotal in Spotify's recommendation system that launched in 2015 and dramatically improved music discovery?

Streaming platforms have revolutionized how we discover music, with sophisticated recommendation algorithms suggesting songs we might love. These AI-powered systems analyze billions of data points to predict your next favorite track. But how well do you understand the machine learning technology that powers your daily soundtrack? Test your knowledge of music industry AI and discover the fascinating technology working behind your playlists!

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Neural networks trained on acoustic waveforms
Collaborative filtering using matrix factorization
Deep convolutional neural networks for audio pattern recognition
Word2vec-inspired models for embedding songs in vector space