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improving music mood classification using lyrics, audio and social tags

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Timbral features are <strong>music</strong>al surface features based on signal spectrum obtained by a Short<br />

Time Fourier Transformation (McEnnis, McKay, Fujinaga, & Depalle, 2005). The most popular<br />

ones are:<br />

1) Spectral Centroid: mean of the amplitudes of the spectrum. It indicates the “brightness” of<br />

a <strong>music</strong>al signal.<br />

2) Spectral Rolloff: the frequency where 85% of the energy in the spectrum is below this<br />

point. It is an indicator of the skewness of the frequencies in a <strong>music</strong>al signal.<br />

3) Spectral Flux: spectral correlation between adjacent time windows. It is often used as an<br />

indication of the degree of change of the spectrum between windows.<br />

4) Average Silence Ratio (also called Low Energy Rate): the percentage of frames with a<br />

less than average energy.<br />

5) MFCCs: st<strong>and</strong>s for Mel Frequency Cepstral Coefficients, the dominant features used for<br />

speech recognition. The mel-frequency cepstrum (MFC) is a representation of the shortterm<br />

power spectrum of a sound, based on a linear cosine transform of a log power<br />

spectrum on a nonlinear mel scale of frequency. The MFC has been proven to<br />

approximate the human auditory system’s response more closely than the normal<br />

cepstrum, <strong>and</strong> MFCCs are coefficients that collectively make up an MFC.<br />

Rhythmic features represent the beat <strong>and</strong> tempo of the <strong>music</strong>al piece. Those can be useful in<br />

<strong>music</strong> <strong>mood</strong> <strong>classification</strong>. Intuitively, fast <strong>music</strong> tends to be exciting rather than relaxing. The<br />

most frequently used rhythmic features include:<br />

25

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