Improved 3D Sound Delivered to Headphones Using Wavelets By Ozlem KALINLI EE-Systems University of Southern California December 4, 2003

Outline:  Introduction  Work  Results  Conclusion

Immersive Audio Environments  Transport listener into the same sonic environment as the event o Multiple, spatially-distributed sound sources oHead and source motion oRoom Acoustics  Virtually listening environments oSynthetic acoustic images (headphones or loudspeakers) oSimulated directional sound information oSimulated room acoustics Introduction Immersive Reproduction of 3D Sound Scheme

Head Related Transfer Function (HRTF)  Head Related Transfer Function (HRTF) Special transformation of a source from a point in free space to the listener’s eardrums.  HRTF measurements are computed using a dummy head (KEMAR)  Used for sound localization Sound Transmission from Source to Listener Introduction

Sound Localization  Localization of sound, cues: oInteraural time difference (ITD), dominant below 1.5 kHz oInteraural intensity difference (IID), dominant above 3 kHz  Reasons: oPath length difference oHead Shadowing oReflection of Head Introduction

Main Work  Goal of Work: To obtain a better sound diffusion from the mono-sound recorded at an anechoic chamber  System Tools o Use HRTF to localize sound, 30 o azimuth, and 0 o elevation oUse wavelet filter banks with time delay at the lowest frequency (below 1.5 kHz) to get the sound diffusion (adding reverberant sound) Work

Overall System Work Fs= 44.1 kHz, 16 bit 5 Stages of dyadic tree to get the signal below 1.5 kHz Daubechies wavelets, with filter tap 16 Delay time 7.25 ms

Simulation Results  4 different types of audio signals are tested Piano, guitar, classical music, pop song  Time Domain Waveforms for Piano Sound (Left Channel) (a) HRTF Sound (b) Delayed Sound with Wavelet (c) Final Sound Results

Results for Piano Sound  Subjective Listening Tests  Relation Between Time Delays and Correlation Coefficient Time Delay [ms] Correlation Coefficient Delayed SoundFinal Sound Results

Other Work Done  Sound localized at 110 o of azimuth with 0 o elevation is also tested, since surround sound is desired at the o and o oListening test results similar to the 30 o of azimuth oRelation Between Time Delays and Correlation Coefficient Time Delay [ms] Correlation Coefficient Delayed SoundFinal Sound Results

Results for Piano Sound  Original sound, Mono  HRTF-30 oTest signal (no delay) oDelayed Sound (7.25 ms) oFinal Sound  HRTF-110 oDelayed Sound (7.25 ms) oFinal Sound 7.25 ms 14.5 ms 17.4 ms 7.25 ms 14.5 ms 17.4 ms Results

Conclusion  Introducing delay in the frequency band below 1.5 kHz produces reverberant sound  The final sound is better than HRTF sound in sense of the sound diffusion.  Depending on the audio characteristic, the optimum delay time to obtain de-correlated sound (small correlation coefficient) may vary.  When the delay is very high, it simulates big halls. Conclusion

References  “Improved 3D Sound Using Wavelets”, U. P. Chong, H. Kim, K. N. Kim, IEEE Information Systems and Technologies,  “HRTF Measurements of a KEMAR Dummy-Head Microphone”, MIT Media Lab Perceptual Computing- Technical Report #280.  “HRTF Measurements of a KEMAR Dummy-Head Microphone”,  “Virtually Auditory Space Generation and Applications”, Simon Carlie, Chapman and Hall, 1996.