Parametric Stereo Coding中參數抽取與聲道合成之設計

Abstract

在低位元音訊壓縮的需求之下，Parametric Stereo Coding (PS)會是一個有幫助的工具。PS的壓縮概念來自於將雙聲道訊號合成為單一聲道訊號，再加上由左右聲道所抽取出的雙聲道特徵來進行壓縮。而在解碼端即可利用單聲道訊號以及抽取的參數來重建回雙聲道訊號。由於所抽取的參數只需要少量的位元需求，所以整體在位元的使用量就可以大幅的降低。對於PS壓縮的設計，本篇論文會著重在參數抽取和聲道合成上。參數抽取控制參數在時間與頻率上的解析度，以達到合適的特徵更新，而聲道合成部份將討論單一聲道訊號的產生辦法。最後在實作方面，由於PS可以架構在HE-AAC之上，讓HE-AAC處理單聲道的壓縮，所以實驗平台將架設在NCTU-HEAAC上。實驗方式會包含主觀測試以及客觀測試兩方面，由這兩種測試來驗證本論文所提出方法的壓縮品質。

Parametric Stereo Coding (PS) tool is an efficient tool for low bit-rate audio compression. It combines the stereo signal into a monaural downmix signal and extracts the parameters of stereo signal as the stereo image. By above information, the PS decoder can reconstruct the stereo signal. Moreover, the stereo parameters requires only a small overhead, the bit usage is substantially decreased. For the design of PS tool, the thesis will focus on the T/F stereo parameter extraction which controls the delivery of stereo parameters both in time domain and frequency domain, and downmix method for generating the monaural downmix signal. Because the PS tool can be jointly used with the HE-AAC for downmix signal encoding, these methods are integrated in the NCTU-HEAAC for implementation and to verify the coding quality. The extensive experiments are executed for both subjective and objective quality measurement in the end of the thesis.