Addressing the Same but different - different but similar problem in automatic music classification

We present a hybrid method in which we classify music from a raw audio signal according to their spectral features, while maintaining the ability to assess similarities between any two pieces in the set of analyzed works. First we segment the audio file into discrete windows and create a vector of triplets respectively describing the spectral centroid, the short-time energy function, and the short-time average zero-crossing rates of each window. In the training phase these vectors are averaged and charted in threedimensional space using k-means clustering. In the test phase each vector of the analyzed piece is considered in terms of its proximity to the graphed vectors in the training set using k-Nearest Neighbor method. For the second phase we apply Foote's (1999) similarity matrix to retrieve the similar content of the music structures between two members in the database. 1. ANALYSIS METHODS 1.1 Spectral Centroid The spectral centroid is commonly associated with the measure of the brightness of a sound. The individual centroid of a spectral frame is defined as (here, F [k] is the amplitude corresponding to bin k in DFT spectrum..) Figure 1 presents the weighted average spectral centroids of the two analyzed sound examples. The lower (magenta) band is an excerpt of the Kremlin Symphony's recording of Mozart's Symphony 25 (K. 183) and the upper (cyan) band is a rock style arrangement of the same musical segment. The high frequency components in the pervasively percussive rock version accounts for its higher placement on the graph. 1.2 Short-Time Energy Function The short-time energy function of an audio signal is defined as: (where x(m) is the discrete time audio signal, n is time index of the short-time energy, and w(m) is a rectangular window.) Time (samples) Figure 1. It provides a convenient representation of amplitude variation over time. Patterns of change over time suggest the rhythmic and periodic nature of the analyzed sound. Figure 2 is the short-time energy change of the same excerpts. The highly fluctuating rock version (cyan) resulting from the persistent drum beats compared to the more subdued but highly contrasting symphonic version suggests one possible determinant for genre classification.