实时语音处理实践指南

本书主要介绍基于互联网场景的交互式实时语音处理流程，内容涉及智能语音助手、智能音箱、音/视频会议等，具体包括实时语音信号处理、数字音效、网络传输编/解码和语音唤醒识别四部分。在阐述各部分的内容时，本书从基本概念和原理入手，将理论和实践相结合，并细致分析了ji具商业价值的实例，以帮助读者了解相关算法在工程上是如何实现的。另外，为便于有兴趣的读者快速进行算法验证并将其改进和应用到实际的项目中，作者也开源了书中算法的源码。 显示全部信息

绪论······································································.1

第1章 信号处理··············································.7

1.1 数字和模拟频率··········································.7

1.2 离散傅里叶变换···········································8

1.2.1 实数DFT ·····································.9

1.2.2 复数DFT ···································.10

1.2.3 负频分量····································.10

1.2.4 DFT变换性质···························.10

1.3 FFT···························································.11

1.3.1 FFT 结果举例····························.12

1.3.2 实信号FFT································.13

1.3.3 短时傅里叶变换························.14

1.3.4 STFT语音窗函数选择··············.14

1.4 重叠相加法和重叠保留法·························.16

1.4.1 OLA············································.17

1.4.2 OLS ············································.19

1.5 加权重叠相加法········································.21

1.5.1 WOLA 计算过程·······················.22

1.5.2 WOLA 窗函数选择···················.22

1.6 滤波器组···················································.23

1.7 语音预加重····································.27

1.8 高斯分布···················································.27

1.8.1 单高斯分布································.27

1.8.2 多维高斯分布····························.29

1.9 HMM模型················································.31

1.10 卡尔曼滤波·············································.32

本章小结·····························································.33

参考文献·····························································.33

第2章 发音机理和器件·······························.34

2.1 语音的产生和接收········································.34

2.1.1 语音产生机理····························.34

2.1.2 发声模型····································.36

2.1.3 发音单位····································.36

2.1.4 发音分类····································.37

2.1.5 声音接收····································.37

2.1.6 声音传播····································.38

2.2 扬声器·······················································.38

2.2.1 电学性能····································.38

2.2.2 声学性能····································.39

2.2.3 底噪············································.40

2.2.4 频响特性····································.41

2.2.5 THD+N POUT···························.41

2.2.6 电压（功率）和失真················.42

2.3 麦克风·······················································.42

2.3.1 麦克风性能指标························.42

2.3.2 麦克风的选择····························.43

2.4 结构设计····················································45

2.4.1 扬声器相关音腔设计················.45

2.4.2 麦克风和扬声器························.45

2.5 音频设备···················································.46

2.5.1 听音设备····································.46

2.5.2 声场表现力································.47

2.5.3 发声设备····································.48

2.5.4 消声室测试································.48

2.6 声学测试···················································.49

2.6.1 声学音量····································.50

2.6.2 失真度THD·······························.50

2.6.3 频响混叠····································.51

2.6.4 麦克风阵列一致性····················.53

2.6.5 AEC参考通路···························.54

2.6.6 扬声器镜频································.56

2.6.7 扬声器最大幅度下的THD·······.57

本章小结·····························································.58

参考文献·····························································.58

第3章 语音端点检测····································.59

3.1 特征选取···················································.59

3.2 判决准则···················································.61

3.2.1 门限············································.61

3.2.2 统计模型法································.61

3.2.3 机器学习法································.62

3.3 VAD 实例·················································.63

3.3.1 高斯分布····································.63

3.3.2 算法流程····································.63

3.3.3 计算流程····································.68

3.4 语音/非语音帧的初始参数························.75

3.4.1 模型参数计算····························.75

3.4.2 高斯混合模型····························.76

3.4.3 EM算法·····································.76

本章小结·····························································.78

参考文献·····························································.78

第4章 单通道降噪········································.79

4.1 谱减法·······················································.79

4.1.1 谱减法原理································.79

4.1.2 谱减法实现································.81

4.1.3 音乐噪声控制····························.83

4.1.4 滤波法········································.83

4.2 维纳滤波···················································.84

4.3 子空间降噪···············································.86

4.4 WebRTC 单通道降噪实现······················.87

4.4.1 算法原理····································.87

4.4.2 算法初始化································.88

4.4.3 信噪比计算：ComputeSnr ·······.90

4.4.4 语音噪声概率计算····················.91

4.4.5 特征选取····································.94

4.4.6 平坦度计算································.96

4.4.7 噪声估计更新函数：

UpdateNoiseEstimate···············.97

4.4.8 消除噪声····································.98

4.4.9 信号合成····································.99

4.4.10 仿真结果··································.99

4.5 深度学习降噪········································.101

本章小结···························································.104

参考文献···························································.105

第5章 声学回声消除·································.106

5.1 回声消除原理·········································.106

5.2 自适应滤波器·········································.108

5.2.1 维纳滤波器······························.108

5.2.2 LMS算法································.109

5.2.3 NLMS算法······························.110

5.2.4 PBFDAF 算法··························.111

5.3 WebRTC 回声消除算法·······················.113

5.3.1 延迟估计··································.113

5.3.2 自适应滤波······························.114

5.3.3 非线性处理（NLP）··············.117

5.3.4 MATLAB代码解读················.118

5.3.5 仿真实验··································.127

5.4 Speex 回声消除算法·····························.128

5.4.1 变步长计算······························.129

5.4.2 双线性滤波器及预处理··········.130

5.4.3 MATLAB代码解读················.132

5.4.4 算法流程示意图······················.141

5.4.5 仿真实验··································.144

本章小结···························································.146

参考文献···························································.146

第6章 声源定位··········································.147

6.1 GCC算法·····················.147

6.2 SRP-PHAT算法··································.149

6.3 MUSIC算法···········································.150

6.4 TOPS 算法·············································.152

6.5 FRIDA算法············································.154

6.6 后处理抗噪·············································.155

6.6.1 统计方法··································.155

6.6.2 卡尔曼方法·······&mid