これまでに我々は,逆ノッチフィルタを利用して音楽信号の基本周波数（音高）を推定する方法を提案した.提案法では,それぞれの音高に対応した複数の逆ノッチフィルタを並列接続し，その出力パワーがしきい値以上となるフィルタから現在の音高を得る.提案法で用いるしきい値の設定は従来，無音区間に基づき設定する固定しきい値であったが,ピアノの鍵盤を叩いた瞬間（打鍵時）に誤判定が生じるという問題があった．そこで，本論文では，適応しきい値を導入し；打鍵時にも対応できるようにする．%We have proposed the method which estimates fundamental frequency (pitch) in musical signal using inverse notch filter. In proposed method, we connect some inverse notch niters in parallel and we can estimate pitches whether the output power of the filter is over the threshold or not. The threshold which have been used in proposed method is a fixed threshold which is based on no sound section, but the fixed threshold has a problem that makes wrong decision when striking the keys of a piano. In this paper, we introduce adaptive threshold to the pitch estimator, and we can cope with when striking the keys of a piano.
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