藉由感知特徵對語音品質做客觀的評量

Abstract

在本論文中，我們使用一個同時考慮時間和頻率上變化的人耳聽覺模型來對語音品質做客觀的評量。我們研究目的是希望可以準確的預測聽者對於語音品質主觀的平均意見分數。客觀的評量主要分為兩種方法：一種是侵入式，另一種是非侵入式。首先，我們會在兩個聽覺感知階段觀察和分析乾淨的語音、加上背景雜訊的語音、以及經過各種不同語音壓縮標準的語音，第一個階段是人耳到中腦的頻譜估計，第二個階段是中腦到大腦皮質聽覺區對時域和頻域同時做分析。其次，我們將從這兩個階段，擷取出在人耳感知上可能影響聽者判斷語音品質好壞的特徵當作參數來對語音品質做客觀評量，這三個特徵分別是－理解性、自然性、基頻失真。最後，我們使用複迴歸分析的方法，將三個特徵參數對語音品質影響的關係做結合，希望藉由這三個基本的特徵參數讓我們能對語音品質的好壞做快速並可靠的評量。

In this study, a joint spectro-temporal auditory model was utilized to assess speech quality objectively. In this model, the first stage is to mimic early cochlear functions of the spectrum estimation and the second stage is to mimic cortical functions of the multi-dimensional spectrum analysis. The goal of this study is to predict subjective mean opinion score (MOS). Objective speech quality assessment can be done by two methods：intrusive and non-intrusive. In this study, firstly, we observe and analyze patterns of the clean speech, the noisy speech with different background noise, and the degraded speech through different codecs at two auditory stages. Secondly, we will derive an objective estimate of the MOS from data-driven perceptual parameters which are believed to reflect people’s judgment on speech quality. Four perceptual parameters considered are intelligibility, naturalness, and pitch distortion. Finally, we use multiple regression analysis to combine the relationship between speech quality and these perceptual parameters, and then obtain our predicted MOS. We then demonstrate the MOS can be characterized quickly and reliably by these three perceptual features.