3D sound reproduction with “OPSODIS” and its commercial applications

1. 3D sound reproduction with “OPSODIS”andits commercial applications Takashi Takeuchi, PhD Chief Technical OfficerOPSODIS Limited Institute of Sound and Vibration Research, University of SouthamptonKajima Technical Research Institute

2. History MSc PhD (Invention) (OPSODIS) OPSODIS Auralisation Joint R&D Joint R&D Stereo Dipole OPSODIS (UK Ltd.)

3. What is OPSODIS™? Optimal Source Distribution • Principle - 3D sound reproduction - Binaural - Loudspeaker reproduction - 2 channel system (3ch option) - Stereo & Surround - reproduction compatible • What is special? - Lossless crosstalk cancellation! - Signal processing by loudspeaker - Good & natural sound quality - Robust control - Elevation (height) reproduction - Multiple listeners

4. Spatial hearing and binaural signal Sound source signal s • Physics source signalpropagationtwo different signal at ears • Perception Separates signal and spatial informationbinaural signals Characteristics of space (physics) （relative position，response of space） Spatial hearing (human) （source position，movement，room size，reverberation） stereo surround A2 binaural A1 d Binaural signals any number of sources …

5. Inverse filtering (crosstalk cancellation) • Loudspeaker reproduction interweaves loudspeaker position • In order to reproduce spatial information arbitrarily, independent transmission to each ear is necessary. • Minimum of two independent (real) sound source necessary C22 Inverse filteringH C12 binaural Signals d Synthesised binaural signals C21 w C11

6. Conventional cross-talk cancellation Cancelling each other Independent control at both ears Right ear t t Left ear Loudspeaker output t t R Right ear L t t Left ear

7. Conventional cross-talk cancellation Independent control at both ears Right ear t t Left ear Loudspeaker output t t R Right ear L t t Left ear

8. Conventional cross-talk cancellation Independent control at both ears Massive destructive interference Right ear t t Left ear Loudspeaker output t t R Right ear L t t Repetitive delay = Large output (Frequency dependent) Left ear

9. Crosstalk cancellation (frequency) phase amplitude Destructive interference at both ears. Inefficient, quality loss, sensitive to errors.

10. Frequency dependency Conventional • from Left SP • from Right SP • reproduced frequency frequency Left ear Right ear

11. Why have 3D systems not performed well so far? Frequency response to listener 6dB (two point sources) (_____) 0dB In-phase signal level (_ _ _) Out-of-phase signal -40dB Frequency (linear) 20kHz 20Hz Sound emitted by loudspeakers do not reach listener’s ears at certain frequencies. Large output required to compensate it.

12. Loss of performance through cross-talk cancellation process • Typical frequency response of the inverse filters for 3D reproduction. 0dB Out-of-phase signal level In-phase signal -40dB 20Hz Frequency 20kHz

13. Loss of performance through cross-talk cancellation process 0dB Original Performance Dynamic range loss = Low Quality ≈ 5 bit Synthesized sound -30dB Distortion Noise Exact matching level Frequency 20kHz 20Hz Cross-talk cancellation degrades performance severely.

14. Analogy to picture quality Reduce; Constant resolution Magnify; Pixel size Quality Loss

15. Loudspeaker span 10° 180° (Stereo Dipole) Original Performance 0 dB ≈ - 3 bit ≈ - 7 bit -16dB Smaller loss More complexity Less complexity -43dB Larger loss Synthesized sound 20Hz 20kHz 20Hz 20kHz frequency (log) frequency

16. Optimal Source Distribution Conventional OPSODIS OPSODIS Conventional Stereo Dipole frequency high low low Transducer position vs Performance (excess amplification) poor 20kHz 2kHz frequency 200Hz 20Hz good 0° 180° 60° 120° transducer position

17. Conventional The worst conditioned frequency dictates performance for all frequencies!! (Stereo Dipole) OPSODIS

18. OPSODIS loudspeaker • Frequency response to listener with OPSODIS. No frequency dependency on amplitude response and phase response OPSODIS 0dB level -40dB frequency

19. OPSODIS principle • Frequency response of the OPSODIS inverse filters. No frequency dependency on amplitude response and phase response 0dB robust • Simple process • No loss resulting from signal manipulations • High quality 3D reproduction • Natural & pure sound quality • Elevation reproduction level -40dB frequency

20. Crosstalk cancellation of OPSODIS Addition Cancellation Independent control at both ears Right ear amplitude phase Left ear R Right ear ½ amplitude, -90º phase ½ amplitude Left ear L Loudspeaker output

21. Crosstalk cancellation of OPSODIS Independent control at both ears Right ear amplitude phase Left ear R Right ear ½ amplitude, -90º phase ½ amplitude Left ear L Loudspeaker output

22. Crosstalk cancellation of OPSODIS Independent control at both ears Right ear amplitude phase Left ear Destructive interference R Right ear ½ amplitude, -90º phase Constructive interference ½ amplitude Left ear L Loudspeaker output Efficient, Lossless, Robust to errors.

23. Reproduction quality Example: 16bit hardware Stereo Dipole frequency frequency ≈17 bit Reproduced dynamic range ≈ +3 dB Reproduced dynamic range ≈ -43 dB 16 bit 16 bit OPSODIS 16 bit 16 bit ≈9 bit • L channel • R channel • reproduced

24. Electro-acoustic transducer for OPSODIS • Flat panel loudspeakers plate high frequency low shaker driving plate narrow width wide • Acoustic waveguide large stiffness small slot driver high frequency low narrow slot wide high frequency low Variation in excited frequency and radiation impedance

25. Discrete system frequency(Hz) transducer span • Width of n enables discretisation • 2 channel, multi-way system • Use of conventional transducers • Wide frequency range • U-shaped valley • Small performance loss

26. Effects of room reflection (sound radiation) Small radiation by OPSODIS Not affected by reflection - dB 0 dB - dB 0 dB 0 dB Reference to radiation by mono loudspeaker • Very large sound radiation other than receiver directions • Needs anechoic room conventional OPSODIS

27. Radiation pattern of Conventional • Radiation pattern is different depending on the frequency. • Single listener． • Very small sweet area. 0dB -∞dB

28. Radiation pattern of OPSODIS • Radiation pattern is constant regardless the frequency; Large sweet area • No spectral change; elevation works everywhere. • Multiple listener listening with a little performance loss. • The interval of L-R cross-talk cancellation is about 0.3m; Alternative seating positions. A B B A A 0.6m 0.6m A: 1 or 3 listener(s) B: 2 listeners

29. Reproduced sound level (lateral position） • 3 seater or 2 seater Left ear signal Right ear signal Lateral position　（m）

30. Aspects of the “OPSODIS” • No dynamic range loss • Quality (Lossless) • Good S/N • No distortion • Robust to errors in plants and filters • Robust to individual difference in HRTFs • Generic inverse filters • Flat amplitude response of inverse filters • Elevation (height etc) works at any location • No colouration at any location • Small sound radiation other than receiver directions • Robust to room reflections • Consistent radiation over frequency • Multiple listener listening

31. 3 channel OPSODIS

32. Inverse filter ~ 2 channel OSD frequency high low low 0dB Out-of-phase component level In-phase component 2ch OSD -40dB Frequency/azimuth

33. Inverse filter ~ 3 channel OSD frequency high low low high low low 0dB Out-of-phase component level In-phase component 3ch OSD -40dB Frequency/azimuth

34. Extension to 3 channel Out-of-phase component 2ch OSD 3ch OSD 2ch 2ch OSD In-phase component 3ch 3ch OSD Singular values of the inverse filter matrix H

35. 3 channel OSD peak (in phase) = valley (out of phase) 3ch OSD 3ch OSD peak (out of phase) = valley (in phase) 2ch OSD excess amplification peak 20kHz 2kHz frequency 2ch OSD 200Hz 20Hz valley 0° 180° 60° 120° transducer azimuth

36. Crosstalk cancellation of 3ch OPSODIS Addition Cancellation Independent control at both ears Right ear amplitude phase Left ear ¼ amplitude, -90º phase Right ear R C ½ amplitude Left ear L ¼ amplitude, +90º phase Loudspeaker output

37. Crosstalk cancellation of 3ch OPSODIS Independent control at both ears Right ear amplitude phase Left ear ¼ amplitude, -90º phase Right ear R C ½ amplitude Left ear L ¼ amplitude, +90º phase Loudspeaker output

38. Crosstalk cancellation of 3ch OPSODIS Independent control at both ears Right ear amplitude phase Destructive interference Left ear ¼ amplitude, -90º phase Right ear R C ½ amplitude Constructive interference Left ear L ¼ amplitude, +90º phase Loudspeaker output Efficient, Lossless, Quality, Robust to errors.

39. Crosstalk cancellation of 3ch OPSODIS Independent control at both ears Right ear amplitude phase Destructive interference Left ear 1/3 amplitude, -120º phase Right ear R C 1/3 amplitude Constructive interference Left ear L 1/3 amplitude, +120º phase Loudspeaker output Efficient, Lossless, Quality, Robust to errors.

40. Summary Combination of signal processing and the new type of loudspeaker based on a new principle • OPSODIS • Enabling high definition 3D sound reproduction with 2 channel (or 3ch) loudspeakers • Natural sound quality without distortion • Natural sound at any location • Effective in any room • Compatible with surround reproduction enables ideal 3D sound delivered to ears.