Evaluating a Simple Approach to Music Information Retrieval: Conceiving Melodic N-Grams as Text

J. Stephen Downie
University of Western Ontario, Canada (July, 1999)


Taking our cue from those printed thematic catalogues that have reduced the amount of music information represented we developed, and then evaluated, a Music Information Retrieval (MIR) system based upon the intervals found within the melodies of a collection of 9354 folksongs. We believe that there is enough information contained within an interval-only representation of monophonic melodies that effective retrieval of music information has been achieved. We extended the thematic catalogue model by affording access to musical expressions found anywhere within a melody. To achieve this extension we fragmented to the melodies into length-n subsections called n-grams. The length of these n-grams and the degree to which we precisely represent the intervals are variables analyzed in this thesis.

N-grams form discrete units of melodic information much in the same manner as words are discrete units of language. Thus, we have come to consider them “musical words.” This implies that, for the purposes of music information retrieval, we can treat them as “real words” and thereby apply traditional text-based information retrieval techniques. We examined the validity of our “musical word” concept in two ways. First, a variety of informetric analyses were conducted to examine in which ways the informetric properties of “musical words” and “real words” are similar or different. Second, we constructed a collection of “musical word” databases using the famous text-based, SMART information retrieval system. A group of simulated queries was run against these databases. The results were evaluated using the normalized precision and normalized recall measures. Results indicate that the simple approach to music information retrieval examined in this study shows great merit.

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