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Listening with Realism: Sound Stage Extension for Laptop Speakers Tsai-Yi Wu Submitted in partial fulfillment of the requirements for the Master of Music in Music Technology in the Department of Music and Performing Arts Professions Steinhardt School New York University Advisor: Dr. Agnieszka Roginska Reader: Dr. Morwaread Farbood December 6, 2013 i This thesis is dedicated to my family. For their endless love, support, and encouragement ii ABSTRACT Abstract Mobile devices with stereo speakers such as laptops are increasingly popular. Even though laptops are mostly used for entertainment, the performance of laptop internal speakers still leaves room for improvement because of the physical constraints. One of the major issues of laptop reproduction is the flat and narrow sound coming from underneath compared to using external speakers. The general approach is to create virtual surround sound speakers by simulating the influence of the shape of human head and pinnae on the sound. However, the ideal listening area of the virtual surround speakers is very narrow in stereo loudspeaker reproduction, and the effect is sensitive to an individual’s body shape. This Master’s thesis introduces a new sound stage width extension method for internal loudspeakers. Ambidio is a real-time application that enhances a stereo sound file playing on a laptop in order to provide a more immersive experience over built-in laptop loudspeakers. The method, based on Ambiophonics principles, is relatively robust to a listener’s head position, and requires no measured/ synthesized HRTFs1. The key novelty of the approach is the pre/post-processing algorithm that dynamically tracks the image spread and modifies it to fit the hardware setting in real-time. Two detailed evaluations are provided to assess the robustness of the proposed method. Experimental results show that the average perceived stage width of Ambidio is 176º using internal speakers, while keeping a relatively flat frequency response and a higher user preference rating. 1 Head Related Transfer Functions, see Section 2.1. i ACKNOWLEDGEMENTS Acknowledgements There are a number of people without whom this thesis might not have been possible written. First and foremost, I would like to thank my advisor, Prof. Dr. Agnieszka Roginska, who has given her valuable time, advice, and warm support to this thesis from the beginning up to the end of the writing. Thank you for your confidence in me. I would also like to thank Mr. Ralph Glasgal, the inventor of Ambiophonics, for his kindly sharing of knowledge and experience. I learned a lot from your insight and I appreciate the patience you showed to me. I would also like to acknowledge Prof. Dr. Morwaread Farbood as the second reader of this thesis for her valuable comments on this thesis. I want to thank Prof. Paul Geluso for his help with the stereo widening techniques, M/S mixing, and reviewing Ambidio. I also want to take this opportunity to thank all of the faculty members of the Department of Music and Performing Arts Professions who have taught and guided me during the years of my study in Music Technology program. I owe particular thanks to E-Ning Chang, Lu-Chin Chu, and JEASMCL for being with me during every darkest night. Thank you for everything. I am also grateful to Shao-Ting Sun and Cheng-I Wang for all the helpful conversations. Being friend with you is one of the best things happened to me in New York. Special thanks goes to Shao-An Juan, who came and rescued me from Hurricane Sandy. To all my friends in Taiwan: Scouts of Chateau Villa, GFN, and 7 Music Studio, thank you all for making me feel like I’m not too far from home. In addition, a thank you to my boyfriend, Pei-Lun Hsieh. Words fail me. I love you. Last but not the least, I would like to give my most sincere gratitude to my beloved family. Thank you for giving me strength to reach for stars. I can’t make it without your support. Words are really not enough to express my gratitude, and I am going to cry because I miss you all so much. I am so blessed to have each and every one of you in my life. I love you all!! ii CONTENTS Contents 1. Introduction ..................................................................................................................................1 1.1 Listening on Laptop Speakers ................................................................................................................1 1.2 Can People Have Better Sound with Laptop Speakers? ...................................................................2 1.3 Chapter Arrangement ..............................................................................................................................3 2. Background ...................................................................................................................................4 2.1 How Humans Locate Sound? .................................................................................................................4 2.2 Stereo Loudspeaker Reproduction ........................................................................................................5 2.3 Spatial Enhancement: Sound Goes Beyond Boundaries ..................................................................6 2.4 Crosstalk and Crosstalk Cancellation ..................................................................................................8 2.5 Mid/Side Processing .............................................................................................................................10 2.6 A Brief Review of Commercial Passive Spatial Enhancement Products .................................11 2.6.1 Qsound Labs, Inc. .................................................................................................................11 2.6.2 Harman International, Inc. ................................................................................................12 2.6.3 DTS, Inc. ................................................................................................................................13 2.6.4 Dolby Laboratories, Inc. ......................................................................................................14 2.6.5 3D3A Lab of Princeton University ................................................................................16 2.6.6 Other Commercial Products ..............................................................................................17 3. Methodology ..............................................................................................................................18 3.1 Whose Ears Should We Listen With? ..............................................................................................18 3.2 Ambiophonics: The Key to Unlock Worlds of Sonic Reality ......................................................19 3.3 Structural design of A new Spatial Enhancement Software: Ambidio .....................................21 3.4 Crosstalk Cancellation Filter Design: Modified RACE Algorithm ...........................................23 3.6 User Interface Design ...........................................................................................................................25 4. Subjective Evaluation ...............................................................................................................27 4.1 Subjective Evaluation Design ..............................................................................................................27 4.1.1 Participants ............................................................................................................................27 iii CONTENTS 4.1.2 Apparatus ...............................................................................................................................28 4.1.3 Process Methods ...................................................................................................................28 4.1.4 Stimuli .....................................................................................................................................29 4.1.5 Procedure ...............................................................................................................................30 4.1.6 Data Analysis .........................................................................................................................32 4.2 Subjective Evaluation Results ..............................................................................................................33 4.2.1 Perceived Stage Width ........................................................................................................33 4.2.2 Perceived Depth and Presence ..........................................................................................35 4.2.3 Sound Quality and Immersion ..........................................................................................38 4.2.4 Preference ...............................................................................................................................40 4.3 Subjective Evaluation Discussion .......................................................................................................42 5. Objective Evaluation .................................................................................................................46 5.1 Objective Evaluation Design ...............................................................................................................46 4.1.1 Apparatus ...............................................................................................................................46