Statistical Modeling and Retrieval of Polyphonic Music
In this article, we propose a solution to the problem of query by example for polyphonic music audio. We first present a generic mid-level representation for audio queries. Unlike previous efforts in the literature, the proposed representation is not dependent on the different spectral characteristics of different musical instruments and the accurate location of note onsets and offsets. This is achieved by first mapping the short term frequency spectrum of consecutive audio frames to the musical space (the spiral array) and defining a tonal identity with respect to center of effect that is generated by the spectral weights of the musical notes. We then use the resulting single dimensional text representations of the audio to create a-gram statistical sequence models to track the tonal characteristics and the behavior of the pieces. After performing appropriate smoothing, we build a collection of melodic n-gram models for testing. Using perplexity-based scoring, we test the likelihood of a sequence of lexical chords (an audio query) given each model in the database collection. Initial results show that, some variations of the input piece appears in the top 5 results 81% of the time for whole melody inputs within a 500 polyphonic melody database. We also tested the retrieval engine for small audio clips. Using 25s segments, variations of the input piece are among the top 5 results 75% of the time.