數位音訊壓縮,由於手機等攜帶式裝置的普及,還有攜帶式裝置的無線上網需求增加,考慮到傳輸時間以及儲存裝置的容量,多數使用者會希望能夠用更小的容量來存放同樣的音樂,因此有更多新的低位元率壓縮方式提出,其中ISO的標準MPEG-4 part 3的Advanced Audio Coding,也在2001年增加了Spectral Band Replication和Parametric Stereo兩個新的模組,以提高低位元率音訊壓縮的壓縮品質。但是在許多Parametric Stereo的聆聽測試中,我們發現有部份經過PS方式壓縮的立體聲音樂,會有空間定位模糊的情形,對此我們希望能夠用軟體運算的方式,來找出有空間定位模糊的部份音樂。 本論文嘗試實作一個立體聲音樂空間定位的軟體評分系統,輸入原始音樂以及壓縮過的音樂,透過兩者的比較,此系統可評斷壓縮過之音樂,是否其空間定位較為模糊。對於不同壓縮方式間空間定位的好壞,當我們能夠透過軟體獲得這些資訊,就可以提供一個相對客觀的評分。
With the growing use of portable devices, the need for wireless connectivity on portable devices is also increasing. Due to the limitation of bandwidth and storage on portable devices, many low bit-rate audio compression methods have been proposed. The amendment of ISO standard MPEG-4 part 3 Advanced Audio Coding (AAC) published in 2001, includes two modules, Spectral Band Replication (SBR) and Parametric Stereo (PS), for enhancing the audio quality at low bit-rates. But according to some listening test reports, stereo music compressed with PS module may blur the spatial sound localization. Therefore, we want a tool to determine whether a piece of music may suffer this problem. In this thesis, we implement a spatial localization quality evaluation system. By giving original audio and compressed audio, the system is able to evaluate the spatial accuracy of the compressed audio. We can give an objective score of spatial quality for different compression methods with software.