Improving Television Sound for People with Hearing Impairments Benjamin Guy Shirley Acoustics Research Centre School of Computing, Science and Engineering College of Science and Technology University of Salford, Salford, UK Submitted in Partial Fulfilment of the Requirements of the Degree of Doctor of Philosophy 2013 Table of Contents Acknowledgements .........................................................................................................................1 Abstract ...............................................................................................................................................2 1.Introduction ..................................................................................................................................3 Research Aim ........................................................................................................................................................3 Thesis Structure ..................................................................................................................................................3 Contribution of the Author .............................................................................................................................5 Deining the Problem ........................................................................................................................................6 Server Side or Client Side Solution ..............................................................................................................6 Digital TV and Surround Sound Broadcast .............................................................................................7 Possibilities Offered by Surround Sound Broadcast ............................................................................8 Dolby Digital Surround Sound ...........................................................................................................8 Multi-channel Audio ............................................................................................................................10 Hearing Impaired (HI) Audio Channel .........................................................................................11 Metadata ...................................................................................................................................................12 Contribution of the Research into Broadcast Standards ...............................................................14 Contribution to Knowledge .........................................................................................................................15 2.Literature Review .....................................................................................................................16 TV Audio for Hearing Impaired People ..................................................................................................16 Hearing Loss and Audio Reproduction ...................................................................................................22 Prevalence of Hearing Loss ..............................................................................................................23 Application of Hearing Aid Processing ........................................................................................25 The Impact of Multichannel Audio ................................................................................................27 Audio for Digital TV Broadcast .................................................................................................................30 Television Audio Systems and Formats ......................................................................................30 Future Developments .........................................................................................................................34 Psychoacoustic Test Methodology ............................................................................................................34 3.The Clean Audio Project Phase 1: Non-Speech Channel Attenuation .....................38 Introduction .......................................................................................................................................................38 Aims of Clean Audio Phase 1 .......................................................................................................................38 Methodology ......................................................................................................................................................39 Audio-Visual Stimuli ............................................................................................................................39 A/B Comparative Tests ......................................................................................................................39 Forced Choice Comparison ...............................................................................................................40 Other Test Design Factors .................................................................................................................40 Interviews with Participants ...........................................................................................................46 Test Material ......................................................................................................................................................46 Analysis of Participants .................................................................................................................................47 ProTile of Hearing Impairments ......................................................................................................47 Setup and Calibration ..........................................................................................................................48 Experimental Results ......................................................................................................................................49 Hearing Impaired Results .................................................................................................................51 Non-Hearing Impaired Results .......................................................................................................52 Signiicance of Results ...................................................................................................................................53 Hearing Impaired Participants .......................................................................................................53 Signiicance: Speech Clarity .............................................................................................................53 Signiicance: Overall Sound Quality ..............................................................................................53 SigniTicance: Enjoyment .....................................................................................................................53 Non-Hearing Impaired Participants .............................................................................................54 Signiicance: Speech Clarity .............................................................................................................54 Discussion ............................................................................................................................................................55 LCR, LCR1, LCR2, C ...............................................................................................................................55 LR (downmixed stereo) .....................................................................................................................55 Analysis of Test Procedures .........................................................................................................................56 Introduction ............................................................................................................................................56 Clip Dependency ....................................................................................................................................57 Playback order .......................................................................................................................................57 Analysis of Test Material ...................................................................................................................59 Visual Cues ...............................................................................................................................................59 Recommendations for Future Test Design ................................................................................61 Conclusions .........................................................................................................................................................62 Downmixed Stereo ...............................................................................................................................62 Level of Left and Right Front Surround Channels ..................................................................63 Summary ..................................................................................................................................................63 Recommendations for Hard of Hearing Viewers Published by Ofcom .....................................64 Further Work .....................................................................................................................................................64