Siri's song recognition feature relies on sophisticated algorithms that analyze the pitch, tempo, and rhythm of your humming or singing to find a match in its vast music database, allowing you to know how to find a classical song by hum. This technology, known as audio fingerprinting, allows Siri to identify songs even if you don't know the lyrics or exact melody.
It's a great tool for discovering new music or recalling forgotten tunes. Keep in mind that while Siri's song recognition is impressive, it may not always be able to identify very obscure or less popular songs. Nevertheless, it's a fun and convenient feature whenever you need to name that tune.