Key Signature identifies the tonal centre of a track — the root note and scale mode (major or minor) around which the harmonic content is organised. SongScore's key detection analyses the frequency distribution of the full audio signal to identify the most harmonically stable pitch centre.
The key signature is important for playlist matching and harmonic compatibility. Many editorial and algorithmic playlists use key as a filter for mood targeting — minor-key tracks tend toward melancholic, dramatic, or tense mood categories, while major-key tracks tend toward happy, uplifting, or romantic categories. Playlist curators often build playlists that maintain a consistent key profile for listening flow.
SongScore detects both the key centre (C, C#, D, etc.) and the mode (major or minor). If a track has ambiguous tonality — common in ambient, experimental, or modal music — SongScore reports the best-fit key with a confidence score. Key detection is also used as an input to BPM and time signature verification, since harmonic rhythm patterns reinforce tempo detection.