對於輕便型音訊裝置在數位音訊的錄放裝置中，如果沒有特殊的低音擴音器或較為昂貴的播放器或耳機，僅利用一般小型多媒體的播放器或耳機播放較低頻的低音是較為困難的。因而眾多文獻指出了低頻頻寬擴展的方法或者可稱作虛擬音高(虛擬低音)，可以在不提高成本的情況下播放出較低頻的低音部份。虛擬音高是利用”遺失基頻”的心理聲學概念去建立的，不過由於當在產生虛擬音高的同時，也會造成非線性失真，導致音訊失真，進而使人類感知聽覺受到影響。因而我們的研究針對虛擬低音中的非線性失真的部份，提出利用小波轉換信號分析的方法，改善其非線性失真所帶來的音訊失真。最後達到優化虛擬低音的目標。

In digital audio playback systems for portable audio device, there is a strong demand to produce deep bass using small multimedia speakers and earphones, without the need for additional subwoofer or expensive speakers/earphones. Therefore, many documents have pointed out the low frequency bandwidth extension method or can be called the virtual pitch (virtual bass), and it can comparatively broadcast out the bass part of low frequency in case of rising cost. The virtual pitch is utilizing and setting up because of ‘missing fundamental’ of the psychoacoustic concept. But because will cause non-linear distortion while producing virtual pitch, causing the audio signal to be distorted, and making the perceptual hearing of human influences. Therefore our research focuses on the non-linear distortion part of virtual bass, utilizing the wavelet transform and improve its non-linear distortion caused the audio signal of distortion. Finally, reach the goal of optimizing virtual bass.

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