音訊編碼之聲音品質研究與分析

Abstract

Windows Media Audio是Microsoft專門為聲音所研究發展的轉碼器，而且通常他的封包都用Advanced Systems Format stream來儲存與表現。每一個Advanced Systems Format的檔案都包含一個或是數個數位影音序列串。Windows Media Video和Windows Media Audio總是包含在Advanced Systems Format的檔案裡一起播放。 Windows Media Audio system使用波形編碼和可變動性長度編碼來達到他的壓縮目標。除此之外，他還使用人類心理聲學模型建立模組來表現在低的取樣速率下也能展現高品質的聲音。 在此篇論文裡，我們扼要地討論關於Advanced Systems Format和Windows Media Audio的解壓縮程序與原理，並且和其他聲音轉碼器所產生的聲音來做音質上的比較，我們的實驗分為主觀測試和客觀測試來討論Windows Media Audio轉碼器和其他聲音轉碼器所分析出來的結果。

Windows Media Audio system is a CODEC designed especially for music and sound, in which packets are saved and showed in Advanced Systems Format stream. And each Advanced Systems Format file consists of one or more digital media streams. Windows Media Video and Windows Media Audio always play in and along with Advanced Systems Format file. Moreover, Windows Media Audio system employs the waveform coding and variable-length coding to achieve its compression. And, applying the mode of human psychoacoustics, it manages to display the high quality of the sample, even at low data rates. In this thesis, an attempt is made to concisely discuss the decoding procedure of Advanced Systems Format and Windows Media Audio, and compare the sound quality with other popular audio CODECs. The experiment aims to employ both Objective and Subjective Quality Measurement, and eventually to arrive at a clarifying analysis on the result of coding quality of Windows Media Audio system.