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improving music mood classification using lyrics, audio and social tags

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achieve very good performance with relatively few training examples, because only support<br />

vectors are taken into account.<br />

Figure 4.2 Support Vector Machines in a two-dimensional space<br />

4.2.2 Algorithm Implementation<br />

The LIBSVM implementation of SVM (Chang & Lin, 2001) is used in this dissertation<br />

research. The LIBSVM package has been widely used in text categorization <strong>and</strong> MIR<br />

experiments, including the Marsyas system, the chosen <strong>audio</strong>-based system for comparisons in<br />

this research (see Section 7.1). The LIBSVM package can output posterior probability of each<br />

testing instance, <strong>and</strong> thus can be adapted for implementing the late fusion hybrid method. The<br />

LIBSVM has a few parameters to set. A pilot study (Hu, Downie, & Ehmann, 2009a) tuned the<br />

parameters <strong>using</strong> the grid search tool in the LIBSVM <strong>and</strong> found the default parameters<br />

performed the best for most cases. Therefore, experiments in this research will use the default<br />

parameters in the LIBSVM. It was also found that a linear kernel yielded similar results as<br />

polynomial kernels. Hence, the linear kernel is chosen for experiments in this research since<br />

polynomial kernels are computationally much more expensive.<br />

51

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