Wavelets in Recognition of Bird Sounds
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Research Article Wavelets in Recognition of Bird Sounds Arja Selin, Jari Turunen, and Juha T. Tanttu Department of Information Technology, Tampere University of Technology, Pori, P.O. Box 300, 28101 Pori, Finland Received 9 September 2005; Revised 30 May 2006; Accepted 22 June 2006 Recommended by Gerald Schuller This paper presents a novel method to recognize inharmonic and transient bird sounds efficiently. The recognition algorithm consists of feature extraction using wavelet decomposition and recognition using either supervised or unsupervised classifier. The proposed method was tested on sounds of eight bird species of which five species have inharmonic sounds and three reference species have harmonic sounds. Inharmonic sounds are not well matched to the conventional spectral analysis methods, because the spectral domain does not include any visible trajectories that computer can track and identify. Thus, the wavelet analysis was selected due to its ability to preserve both frequency and temporal information, and its ability to analyze signals which contain discontinuities and sharp spikes. The shift invariant feature vectors calculated from the wavelet coefficients were used as inputs of two neural networks: the unsupervised self-organizing map (SOM) and the supervised multilayer perceptron (MLP). The results were encouraging: the SOM network recognized 78% and the MLP network 96% of the test sounds correctly. Copyright © 2007 Arja Selin et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
Nearly all birds make different kinds of sounds which are used in communication with other conspecifics and also between different species. Sounds are only produced when needed, and so all the sounds have some meaning [1, 2]. Most sounds are produced by the syrinx, which is the avian vocal organ [3]. In most species the syrinx is bipartite, so the bird can produce two notes simultaneously [4, 5]. Bird sounds can be tonal or inharmonic, which is one way to divide the bird species into groups. Inharmonic sounds are often transient and their frequency contents are very near each other. Bird vocalization contains both songs and calls. Calls are shorter and simpler than songs, and both sexes produce them throughout the year. It seems that most birds have from 5 to 15 distinct calls, and the functions of them can be, for example, flight, alarm, excitement, and so on. Some birds can have several different calls for the same function, whereas some birds use very similar calls in different circumstances to mean different things. In addition, in many species there is high individual and regional variability in phrases and song patterns [6–9]. Thus, two kinds of bird sound variability have to be taken into account in the classification. One is the variation of different sound types and another is the variation across geographic regions and among individuals.
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