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198 Music Emotion Recognition
Genre and emotion provide complementary descriptions of music content and
often correlate with each other. For example, a rock song is often aggressive, whereas
a rhythm and blues (R&B) song is more likely to be sentimental. Despite the salient
correlation between genre and emotion, genre classification and emotion classifica-
tion are often studied separately without considering the interrelation.
This chapter describes a two-layer music emotion classification scheme that ex-
ploits the correlation between genre and emotion . The genre metadata are used
to aid emotion classification because genre metadata are easier to collect and because
genre classification is relatively easier. Specifically, the genre of a song is predicted
in the first layer, and then the genre-specific emotion classification model is applied
in the second layer to predict the emotion of the song, as shown in Figures 12.1(b)
and (c). Experimental results are provided to show the superiority of the two-layer
music emotion classification scheme over the traditional single-layer scheme.
12.2 Two-Layer Music Emotion Classiﬁcation
The main idea of the two-layer emotion classification scheme is to group songs by
genre and train an emotion classifier specifically for songs of each genre. The use of
such genre-specific classifiers is motivated by the following two observations. First,
since emotion and genre are correlated, we may set up different emotion priors for
each genre-specific classifier. For example, a rap song is less likely to be relaxing than
a jazz song. Second, as a happy song of rock music and a happy song of jazz music
may sound substantially different, emotion classification may become easier if each
genre-specific classifier only needs to focus on a single genre of music.
As shown in Figure 12.1(a), a typical single-layer emotion classification system
is composed of two parts: feature extraction and emotion classification. An emotion
Te st music Test music Test music
being each genre
(a) (b) (c)
Figure 12.1 Schematic diagrams of (a) the traditional single-layer emotion clas-
siﬁcation scheme, (b) the proposed two-layer scheme hardGenre, and (c) the soft
version of the two-layer scheme softGenre.