It normally applies to songs or other music with a distinct single theme or melody.
The system involves taking a user-hummed or whistled melody (input query) and comparing it to an existing database.
The system then returns a ranked list of music closest to the input query.
The MPEG-7 standard includes provisions for QbH music searches.
Examples of QbH systems include ACRCloud, SoundHound, Musipedia, Tunebot and Google Search.