Improved 3D Sound Delivered to Headphones Using Wavelets

1
Improved 3D Sound Deliveredto Headphones Using
Wavelets

• By
• Ozlem KALINLI

EE-Systems University of Southern
California December 4, 2003
2
Outline

• Introduction
• Work
• Results
• Conclusion

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Immersive Audio Environments
Introduction

• Transport listener into the
• same sonic environment as
• the event
• Multiple, spatially-distributed
• sound sources
• Head and source motion
• Room Acoustics
• Virtually listening environments
• Synthetic acoustic images
• (headphones or loudspeakers)
• Simulated directional sound
• information
• Simulated room acoustics

Immersive Reproduction of 3D Sound Scheme
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Head Related Transfer Function (HRTF)
Introduction

• Head Related Transfer Function (HRTF)
• Special transformation of a source from a
  point in free space to the listeners eardrums.
• HRTF measurements are computed using a dummy head
  (KEMAR)
• Used for sound localization

Sound Transmission from Source to Listener
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Sound Localization
Introduction

• Localization of sound, cues
• Interaural time difference (ITD) , dominant below
  1.5 kHz
• Interaural intensity difference (IID), dominant
  above 3 kHz
• Reasons
• Path length difference
• Head Shadowing
• Reflection of Head

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Main Work
Work

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

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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

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Simulation Results
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
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Results for Piano Sound
Results

• Subjective Listening Tests
• Relation Between Time Delays and Correlation
  Coefficient

Time Delay ms Correlation Coefficient Correlation Coefficient
Time Delay ms Delayed Sound Final Sound
7.25 -0.3994 0.3577
14.5 -0.3235 0.3002
17.4 -0.3566 0.3377
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Other Work Done
Results

• Sound localized at 110o of azimuth with 0o
  elevation is also tested, since surround sound is
  desired at the 110o and - 110o
• Listening test results similar to the 30o of
  azimuth
• Relation Between Time Delays and Correlation
  Coefficient

Time Delay ms Correlation Coefficient Correlation Coefficient
Time Delay ms Delayed Sound Final Sound
7.25 -0.2905 -0.0803
14.5 -0.2024 -0.1194
17.4 -0.2894 -0.1254
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Results for Piano Sound
Results

• Original sound, Mono
• HRTF-30
• Test signal (no delay)
• Delayed Sound (7.25 ms)
• Final Sound
• HRTF-110
• Delayed Sound (7.25 ms)
• Final Sound

7.25 ms 14.5 ms 17.4 ms
7.25 ms 14.5 ms 17.4 ms
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Conclusion
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.

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References

• Improved 3D Sound Using Wavelets, U. P. Chong,
  H. Kim, K. N. Kim, IEEE Information Systems and
  Technologies, 2001.
• HRTF Measurements of a KEMAR Dummy-Head
  Microphone, MIT Media Lab Perceptual Computing-
  Technical Report 280.
• HRTF Measurements of a KEMAR Dummy-Head
  Microphone, http//sound.media.mit.edu/KEMAR.html
  
• Virtually Auditory Space Generation and
  Applications, Simon Carlie, Chapman and Hall,
  1996.