Thesis Committee Members: 
Ken Pohlmann (Chair, MUE),    Colby Leider (MUE),    Dr. Mohamed Abdel-Mottaleb (EEN),     Dr. Edward Asmus (Associate Dean)

This research was supported by Delphi Automotive Systems
Special thanks to MUE Alumni Kevin Heber from Delphi!

Table of Contents

                       Abstract
                       Acknowledgment
                       Dedication
                       List of Figures
                       List of Tables

                       Chapter 1: Introduction

                       Chapter 2: Localization
                                                     Interaural Difference Cues
                                                      Monaural Cues
                                                      Localization Blur

         Chapter 3: Localization Cue Salience
                                                     Physical Aspects
                                                     Perceptual Aspects

                      Chapter 4: Auditory Scene Analysis  
                                                     Precedence Effect
                                                     Auditory Stream Segregation
                                                     The Acoustic Space

                      Chapter 5: Experimentation
                                                     Experimental Conditions
                                                      Test Signals
                                                      Experimental Variables
                                                    Test Methodology
                                         Test Equipment

                      Chapter 6: Results and Analysis  
                                                     Experimental Results
                                              Analysis
                                                     Analysis - Loudness Calculations
                                             Analysis - Loudness Experiments
                                             Analysis - ABX Testing

                      Chapter 7: Conclusions and Recommendations

                      References
                      Appendix              
                                                    Appendix A- Full Data Set - Listening Tests I
                                                    Appendix B- Full Data Set - Listening Tests II
                                                    Appendix C- Matlab Files
                                                    Appendix D - Impulse Response
                                                    Appendix E - Loudspeaker Frequency Response  

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ABSTRACT

The ability of humans to detect the location of a sound is generally referred to as localization.  Sound waves interact with the head, body, and pinnae creating temporal and spectral differences between the left and right ear canal signals.  The brain uses these differences to interpret a probable number of sound events and their respective locations.  There are three major cues: interaural time differences (arrival, phase, envelope), interaural level differences, and the monaural pinnae influences.  The physical presence of these cues depends mostly on the spectral content of the sound and its spatial origin relative to the listener.  Perceptually, the localization cues exhibit a relative dominance that varies significantly with frequency.  This research explores the relative importance of low and high frequency localization cues during free field listening.  More specifically, it compares the horizontal shift of a stereo image caused by spatially relocating low versus high frequency bands of the audible spectrum.  It is shown that contrary to the popular belief that low frequencies are “hard to localize,” the horizontal position of a stereo image is most significantly affected by moving low-to-mid frequencies as opposed to high frequencies.  This can most likely be attributed to the overall perceptual dominance of low frequency interaural phase differences.

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DEDICATION

This work is dedicated to all of those around me who unselfishly gave their support and understanding while I completed this thesis.  First, I send all my love and appreciation to my immediate family who have been my biggest fans while also challenging me to accept nothing less than my dreams.  To my parents, whose hard-working attitude and modest lifestyle have taught me to work for what I want and be generous with what I have.  To my little sister, who has encouraged my successes and maintained a loving relationship despite our differences.  To Amy Beth, thank you for all of your sacrifices, and for being pleasant in a difficult situation - this would have been a lot tougher without your support.  Finally, to my grandparents and extended family - thank you for staying involved in my life and always being there to tell me how proud you were.  Your love and kindness has shaped the person that I am today, and given me the confidence and determination to complete this project.

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ACKNOWLEDGMENT

 I would like to especially thank my advisor and mentor, Ken Pohlmann, who has generously given of his precious time and provided me with several great opportunities during my time at UM; I hope we will again work together on future projects.  To Kevin Heber of Delphi Automotive Systems, who took the initiative to get involved with my research and provided useful equipment and financial contributions.  Thank you also to my thesis committee, for their time and cooperation with this work.  Of course this research would not have been possible without all of the student volunteers who generously gave their time with minimal begging on my part.  Also to the faculty and staff of UM including Joe Abbati, Luis Ruiz, and Paul Griffith who were flexible enough with equipment, facilities and schedules to allow me to complete the needed listening tests.

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 List of Figures

Figure 1: Views of a listener from the Rear (left) and Top (right) and the spatial relocation of high (H), mid (M), and low (L) frequencies.  Shown are typical (a) Stereo,  (b) Automotive, and (c) Home Theater Surround loudspeaker systems  

Figure 2: Preliminary experiments tested “mono-ized” high frequencies

Figure 3: Views of the auditory planes, azimuth angle and elevation angle

Figure 4: ITDs are caused primarily by path length differences

Figure 5: Interaural Phase Difference (IPD) has two physical values due to periodicity

Figure 6: Interaural Envelope Time Difference (IETD) also has two physical values due to periodicity

Figure 7: Interaural Level Differences caused by reflection of sound off head is (a) minimal for low frequencies (b) significant for high frequencies

Figure 8: The cone of confusion is a set of points which provides identical interaural cues

Figure 9: Horizontal plane localization of sinusoidal  (solid) and narrow band noise (dotted) as compared to a reference sound of wide-band noise at 0, 40, and 320 degree azimuth locations.  Shown versus frequencies to 5 kHz.  Reprinted from Blauert (1999) with permission from the MIT press

Figure 10: ITD and ILD variations with speaker position (azimuth)

Figure 11: IATD varies only with position, while IPD varies with position and signal frequency.  Shown for (a) low frequency source (b) high frequency source (c) high frequency source with new spatial  location

Figure 12: Complex patterns of ILD (left) and ITD (right) with varied horizontal plane positions (azimuth).  Reprinted from Blauert (1999), with permission from the MIT press

Figure 13: Generic (a) Physical and (b) Perceptual localization cue salience versus frequency

Figure 14: Physical setup of test

Figure 15: Spectrogram of music passage L (top) and R (bot)

Figure 16: Music passage temporal (top) and total energy (bottom)

Figure 17: Music passage’s subband energy.

Figure 18: Music passage’s combined subband energy

Figure 19: Spectrogram of white noise passage

Figure 20: Division of Frequencies between L and SR speaker

Figure 21: Gusman "dead" room basic dimensions

Figure 22: Electrical schematic of test setup

Figure 23: Arcade’s Main Program Screen

Figure 24: Arcade’s Amplifier Configuration screen with 8 selector bars (at top)

Figure 25: Music Image Summary

Figure 26: Band E vs. Music Image

Figure 27: Band DE vs. Music Image

Figure 28: Band CDE vs. Music Image

Figure 29: Noise Image Summary

Figure 30: Band E vs. Noise Image

Figure 31: Band DE vs. Noise Image

Figure 32: Band CDE vs. Noise Image

Figure 33: Shift hierarchy of SR bands for Music track

Figure 34: Shift hierarchy of SR bands for Noise track

Figure 35: Listening Test II Setup

Figure 36: Loudness Comparisons of Low Frequency Bands with High pass (left) and High Frequency Bands with Low pass (right)

Figure 37: Spectrogram of Track One - Madonna

Figure 38: Spectrogram of Track Two - What is Hip?

Figure 39: Spectral Energy for Track One - Madonna

Figure 40: Spectral Energy for Track Two - What is Hip?

Figure 41: “Dead” room Impulse Response Setup

Figure 42: “Free field” Impulse Response Setup

Figure 43: Temporal Plots of Impulse Responses

Figure 44: Spectral Plots of “Room” (top) and “Field” Impulse Response

Figure 45: Resulting Impulse Responses of  “Room"

Figure 46: Frequency response measurement setup

Figure 47: Frequency Response of MPS-1610 Loudspeakers

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List of Tables

Table 1: Trial subband variables

Table 2: Significance levels for Music test results

Table 3: Significance levels for Noise test results

Table 4: ISO 266 Octave Band Frequency Centers

Table 5: Level of Spatially Relocated Bands

Table 6: Calculated Octave Band Levels

Table 7: Loudness Index values from table lookup

Table 8: Final calculated loudness levels

Table 9: Band A vs. Bandwidth Loudness

Table 10: Band AB vs. Bandwidth Loudness

Table 11: Band E vs. Bandwidth Loudness

Table 12: Band DE vs. Bandwidth Loudness

Table 13: Band CDE vs. Bandwidth Loudness

Table 14: ABX Test Results

Table 15: Energy Analysis of misc. music tracks at 10 kHz

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Created  February 2003 by Rob Hartman

Copyright (C) 2003