Head-Related Transfer Function and Acoustic Virtual Reality (eBook)

Preface 5
Contents 7
Chapter 1: Introduction 11
1.1 Why Research HRTFs 11
1.2 What Is an HRTF? 12
1.3 HRTF and HRIR 13
1.4 Sound Source and Sound Image 14
1.5 Coordinate System 15
1.6 Brief History of HRTF Research - Current Achievements and Research Questions to Be Settled 17
1.6.1 Origin of the HRTF 17
1.6.2 Physical Characteristics of the HRTF 17
1.6.3 Reproduction of the Direction of a Sound Image by Reproduction of the HRTF 18
1.6.4 Cues for the Perception of Lateral Direction 18
1.6.5 Cues for the Perception of Vertical Direction 18
1.6.6 Physiological Mechanism for the Perception of the Direction of a Sound Image 19
1.6.7 HRTF Models 19
1.6.8 Standardization of the HRTF 20
1.6.9 Individualization of the HRTF 20
1.6.10 Measurement of the HRTF 21
1.6.11 Numerical Calculation of the HRTF 21
1.6.12 Directional Band 21
References 22
Chapter 2: HRTF and Sound Localization in the Horizontal Plane 25
2.1 HRTF in the Horizontal Plane 25
2.2 Sound Localization in the Horizontal Plane 26
2.2.1 Localization Using the listener´s Own HRTFs 26
2.2.2 Localization Using Others´ HRTFs 28
2.3 Cues for Lateral Localization 29
2.3.1 Interaural Time Difference (ITD) 30
2.3.2 Interaural Level Difference (ILD) 31
2.4 Cone of Confusion 32
2.5 Summing Sound Image Localization Using Multiple Sound Sources 33
References 34
Chapter 3: HRTF and Sound Localization in the Median Plane 35
3.1 HRTFs in the Median Plane 35
3.2 Sound Localization in the Median Plane 36
3.2.1 Localization Using listener´s Own HRTFs 36
3.2.2 Localization Using Others´ HRTFs 38
3.2.3 Three Major Errors Regarding Sound Localization in the Median Plane 40
3.3 Cues for Vertical Localization 41
3.3.1 Overview of Spectral Cues 41
3.3.2 Details of Spectral Cues 41
3.4 Role of Spectral Information at both Ears in Median Plane Localization 48
3.5 Origin of Spectral Cues 51
3.5.1 Contribution of Pinnae 51
3.5.2 Origin of Peaks 55
3.5.3 Origin of Notches 59
3.6 HRTF Learning by Subjects 61
3.7 Knowledge of Sound Source 63
3.8 Physiological Mechanism of Notch Detection 64
3.9 Head Movement 64
References 65
Chapter 4: Individuality of HRTF 68
4.1 Individual Differences in HRTFs 68
4.1.1 Individual Differences in Amplitude Spectra 68
4.1.2 Individual Differences in Spectral Cues 70
4.1.3 Individual Differences in Interaural Time Difference 71
4.1.4 Individual Differences in Interaural Level Difference 72
4.2 Individual Differences in the Pinna and Head Shape 75
4.2.1 Individual Differences in Pinna Shape 76
4.2.2 Individual Differences in Head Shape 77
4.3 Standardization of HRTFs 79
4.3.1 Sound Image Localization with the HRTFs of a Dummy Head 79
4.3.2 Sound Image Localization Using Robust HRTF Sets 82
4.4 Individualization of HRTFs 91
4.4.1 Individualization of Amplitude Spectra of HRTFs 92
4.4.2 Measures for Physical Evaluation of Individual Differences of HRTFs 103
4.4.3 Individualization of ITD 105
4.4.4 Individualization of ILD 108
4.4.5 Expected Future Development 111
References 112
Chapter 5: HRTF and Sound Image Control for an Arbitrary Three-Dimensional Direction 115
5.1 Spatial Interpolation of HRTF 115
5.2 Similarity of Notches and Peaks Among Sagittal Planes 116
5.3 Three-Dimensional Sound Image Control Using the Median Plane HRTFs and Interaural Differences 119
5.3.1 Three-Dimensional Sound Image Control Using the Measured HRTFs in the Median Plane and Interaural Differences 119
5.3.2 Three-Dimensional Sound Image Control Using the Parametric HRTFs in the Median Plane and Interaural Differences 122
5.3.3 Three-Dimensional Sound Image Control Using the Best-Matching HRTF and the ITD 124
5.4 Summing Localization Between Sagittal Planes 125
References 128
Chapter 6: Directional Band and Spectral Cue 130
6.1 Directional Band 130
6.2 Individual Differences in Directional Bands 130
6.3 Band Widths of Directional Bands 131
6.4 Relationship Between Directional Band and Spectral Cue 135
References 135
Chapter 7: Distance Perception and HRTF 136
7.1 Sound Source Distance and Sound Image Distance 136
7.2 Physical Characteristics that Affects Sound Image Distance 137
7.2.1 Sound Pressure Level 137
7.2.2 Time Delay of Reflections 139
7.2.3 Incident Direction 139
References 148
Chapter 8: Speech Intelligibility and HRTF 149
8.1 Binaural Masking Level Difference 149
8.2 Influence of Incident Direction on Word Intelligibility 150
References 153
Chapter 9: Measurement Method for HRTF 154
9.1 Configuration of the Measurement System 154
9.2 Measurement Signal 154
9.3 Loudspeakers 158
9.4 Microphones 158
9.5 Subjects 159
9.6 Derivation Method for HRTFs 160
9.7 Short-Time HRTF Measurement Method 161
References 161
Chapter 10: Signal Processing of HRTF 162
10.1 Method for Calculating the ITD and the ILD 162
10.2 Extracting Method of Spectral Cues 163
10.3 Method for Convolution of the HRIR and Sound Source Signal 167
10.3.1 Calculation in the Time Domain 167
10.3.2 Calculation in the Frequency Domain 169
References 174
Chapter 11: Comparison of HRTF Databases 176
11.1 Representative HRTF Database 176
11.2 Comparison of Spectral Cues 177
11.3 Comparison of Pinna Shape 179
References 182
Chapter 12: Principle of Three-Dimensional Sound Reproduction 183
12.1 Reproduction of Ear Input Signals through Headphones 183
12.1.1 Basic Principle 183
12.1.2 Accuracy of Sound Image Localization 189
12.1.3 Introduction of Dynamic Cue 190
12.2 Reproduction of Ear-Input Signals with Two Loudspeakers 192
12.2.1 Basic Principle 192
12.2.2 Accuracy of Sound Image Localization 195
References 198
Chapter 13: Acoustic VR System 199
13.1 System Configuration 199
13.2 Signal Processing Flow 201
13.3 Application to Concert Hall Acoustics 202
13.4 Application to a Public Address System 204
13.5 Application to Searching for a Sound Source Direction 206
References 209
Appendixes 210
Appendix 1 Perception of Direction of an Actual Sound Source 210
Localization in the Horizontal Plane 210
Localization in the Median Plane 211
Just Noticeable Difference in Perception of Direction 212
Appendix 2 Transmission Path of Sound Waves 213
Room Impulse Response 213
Head-Related Impulse Response 215
Binaural Room Impulse Response 215
Ear Canal Impulse Response 216
Summary of the Transmission Path 217
Appendix 3 Prediction Method of Room Acoustics 217
Numerical Calculation 217
Image Method 218
Ray Tracing Method 219
Numerical Calculation Method Considering the Wave Property of Sound 220
Scale Model Experiment 220
Appendix 4 Time Window 220
Rectangular Window 221
Hanning Window 221
Hamming Window 221
Blackman Window 222
Blackman-Harris Window 223
Appendix 5 Method for Making an Earplug-Type Microphone 226
Making an Ear Mold 226
Materials and Equipment 226
Procedure for Making a Reverse Ear Mold 226
Procedure for Making the Final Mold 229
Making a Microphone 231
Materials and Equipment 231
Preparation of a Microphone 232
Making an Earplug-Type Microphone 233
Appendix 6 HRTFs Using 96-kHz Sampling 234
References 235
Index 236