Which machine learning technique is NOT commonly used by major music streaming services to generate personalized song recommendations?

The modern music industry relies heavily on machine learning algorithms to deliver personalized experiences to listeners. These sophisticated systems analyze listening patterns and preferences to recommend new artists and songs. But how well do you understand the technology that powers your favorite music streaming platforms? Test your knowledge of music industry machine learning with this challenging question!

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Natural Language Processing (NLP) analysis of song lyrics
Collaborative filtering based on similar users' listening habits
Facial recognition monitoring of listeners' emotional responses
Audio signal processing to identify acoustic similarities between tracks