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  • Research Article
  • Open Access

Real-Time Audio-to-Score Alignment Using Particle Filter for Coplayer Music Robots

  • 1Email author,
  • 2, 3,
  • 1,
  • 1 and
  • 1
EURASIP Journal on Advances in Signal Processing20102011:384651

  • Received: 16 September 2010
  • Accepted: 2 November 2010
  • Published:


Our goal is to develop a coplayer music robot capable of presenting a musical expression together with humans. Although many instrument-performing robots exist, they may have difficulty playing with human performers due to the lack of the synchronization function. The robot has to follow differences in humans' performance such as temporal fluctuations to play with human performers. We classify synchronization and musical expression into two levels: (1) melody level and (2) rhythm level to cope with erroneous synchronizations. The idea is as follows: When the synchronization with the melody is reliable, respond to the pitch the robot hears, when the synchronization is uncertain, try to follow the rhythm of the music. Our method estimates the score position for the melody level and the tempo for the rhythm level. The reliability of the score position estimation is extracted from the probability distribution of the score position. The experimental results demonstrate that our method outperforms the existing score following system in 16 songs out of 20 polyphonic songs. The error in the prediction of the score position is reduced by 69% on average. The results also revealed that the switching mechanism alleviates the error in the estimation of the score position.


  • Probability Distribution
  • Information Technology
  • Tempo
  • Quantum Information
  • Temporal Fluctuation

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Authors’ Affiliations

Graduate School of Informatics, Kyoto University, Kyoto 606-8501, Japan
Honda Research Institute Japan, Co., Ltd., Wako, Saitama 351-0114, Japan
Graduate School of Information Science and Engineering, Tokyo Institute of Technology, Tokyo 152-8550, Japan


© Takuma Otsuka et al. 2011

This article is published under license to BioMed Central Ltd. 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.