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.