3D聲音訊號處理實現於汽車音訊:以單麥克風背景噪音估測為基礎之適應性音訊增益控制器

Abstract

本論文的研究著重於提升汽車音訊的聆聽品質。現今車內的多聲道視聽系統進展的十分快速，然而，汽車內部仍然因為一些背景噪音像引擎、震動、冷氣而被視為不良的聆聽環境。再來敘述一些可以在車內惡劣環境下拓展頻寬以及提升聆聽品質的聲音系統。本研究提出三個方法在車內產生聲音特效，第一、二部份分別敘述虛擬重低音(VB)以及語音清晰化(VC)的方法，它們分別闡述將頻寬往低頻拓展以及強調中頻的技術。第三部份提出聲道拓展/壓縮，提出如何針對狹小且反射多的環境提供較好的聲場。本研究也提出了一個新的系統，運用噪音估測系統(NLE)結合動態控制系統(DRC)來適應性的調整汽車音訊系統的增益。此方法運用了兩個系統，首先使用最小均方(LMS)演算法來估測背景噪音的大小，之後計算先驗的訊噪比(SNR)再根據事先設計的靜態曲線(Static curve)可以得到適應性調整後的增益。

A comprehensive study was conducted to improve the listening quality of automotive audio. There is increased proliferation nowadays of multichannel audiovisual systems used in cars. However, the interior of a car is known as a notorious listening environment due to background noise like engine, vibration and air conditioning. It is then desirable to develop audio systems that are capable of extending the bandwidth and improving the audio quality in harsh car environments. This study brings three approaches to generate the audio effect in a car. First and second section is virtual bass (VB) and voice clarity (VC), describes the bandwidth expansion toward the low-frequency and emphasizes the middle-frequency. Third section is updownmix, describes how to render spatial sound field to cope with the reflections in the confined space. This study also proposes a new system that makes use of a Noise Level Estimator (NLE) combines Dynamic Range Control (DRC) to adaptively adjust the gain of an automotive audio system. NLE and DRC are used in the system for noise estimation and automatic gain control, respectively. The system needs one microphone to receive the noisy signal. Background noise level is estimated by a system that uses Least-Mean-Squares (LMS) algorithm and then calculated a priori signal to noise ratio (SNR). According to the static curve designed in advance, the gain of the audio input can be adjusted dynamically based on the SNR determined. These processing algorithms have been practically implemented on a car. Simulations and experiments were conducted for validating the proposed adaptive audio gain control systems.