Comparison of dictionary-based approaches to automatic repeating melody extraction

Automatic melody extraction techniques can be used to index and retrieve songs in music databases. Here, we consider a piece of music consisting of numerical music scores (e.g. the MIDI file format) as the input. Segmentation is done based on the tempo information, and a music score is decomposed into bars. Each bar is indexed, and a bar index table is built accordingly. Two approaches were proposed to find repeating patterns by the authors recently. In the first approach, an adaptive dictionary-based algorithm known as the Lempel Ziv 78 (LZ-78) was modified and applied to melody extraction, which is called the modified LZ78 algorithm or MLZ78. In the second approach, a sliding window is applied to generate the pattern dictionary. It is called the "Exhaustive Search with Progressive LEngth" algorithm or ESPLE. Dictionaries generated from both approaches need to be pruned to remove non-repeating patterns. Each iteration of either MLZ78 or ESPLE is followed by pruning of updated dictionaries generated from the previous cycle until the dictionaries converge. Experiments are performed on MIDI files to evaluate the performance of the proposed algorithms. In this research, we compare results obtained from these two systems in terms of complexity, performance accuracy and efficiency. Their relative merits and shortcomings are discussed in detail.