Time Series Representations for Music Information Retrieval

Time series representations are common in MIR applications such as query-by-humming, where a sung query might be represented by a series of ‘notes’ for database retrieval. While such a transcription into (pitch, duration) pairs is convenient and musically intuitive, there is no evidence that it is an optimal representation. The present work explores three time series representations for sung queries: a sequence of notes, a ‘smooth’ pitch contour, and a novel sequence of pitch histograms. Dynamic alignment procedures are described for the three representations. Multiple continuity constraints are explored and a modified dynamic alignment procedure is described for the histogram representation. We measure the performance of the three representations using a collection of naturally sung queries applied to a target database of varying size. The results show that the note representation lends itself to rapid retrieval whereas the contour representation lends itself to robust performance. The histogram representation yields performance nearly as robust as the contour representation, but with computational complexity similar to the note representation.