Audio rendering: from sound diffusion to sound projection

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Audio rendering: from sound diffusion to sound projection

  1. 1. Audio rendering: from sounddiffusion to sound projectionRoberto Magalotti, B&C SpeakersAugusto Sarti, Politecnico di Milano
  2. 2. B&C Speakers is... ... one of the largest and most prestigious electroacoustic transducer manufacturers in the world; designing, developing and manufacturing only for the high-end professional audio market under its own ‘B&C Speakers’ brandname2 Roberto Magalotti - Augusto Sarti
  3. 3. Summary •  Loudspeakers §  A bit if history §  Loudspeakers today •  Directivity in acoustics §  Definition §  Specification §  Examples •  Line arrays in sound reinforcement §  In the 50 §  In the 90 §  Today •  What processing can do •  Spatial audio •  Acoustic holography •  Room compensation •  Virtual acoustics •  Technological and scientific challenges3 Roberto Magalotti - Augusto Sarti
  4. 4. A bit of History… •  1857, Antonio Meucci invents the “Telettrofono”, which includes the first loudspeaker •  “consiste in un diaframma vibrante e in un magnete elettrizzato da un filo a spirale che lo avvolge. Vibrando, il diaframma altera la corrente del magnete. Queste alterazioni di corrente, trasmesse allaltro capo del filo, imprimono analoghe vibrazioni al diaframma ricevente e riproducono la parola” •  1876, Alexander Graham Bell patents Meucci’s invention The US congress finally recognizes Meucci’s paternity of the invention in 20024 Roberto Magalotti - Augusto Sarti
  5. 5. A bit of History… •  1877, Ernst Siemens (Germany) patented the first loudspeaker •  1898, Sir Oliver Lodge (England) second patent for a loudspeaker (before music was electrified)5 Roberto Magalotti - Augusto Sarti
  6. 6. A bit of History… •  1924, two General Electric researchers, Chester W. Rice and Edward Washburn Kellogg patented the Radiola speakers (moving coil, direct radiator loudspeaker)6 Roberto Magalotti - Augusto Sarti
  7. 7. A bit of History… •  1926, two researchers from Bell Labs, E.C. Wente and A.L. Thuras, designed a “phase plug” in front of the membrane of a horn-loaded loudspeaker, creating the compression driver7 Roberto Magalotti - Augusto Sarti
  8. 8. A bit of History... •  1954, Edgar Villchur of Acoustic Research developed the acoustic suspension principle for loudspeaker enclosure deisgn8 Roberto Magalotti - Augusto Sarti
  9. 9. A bit of History... •  1957, Quad ESL marketed as the first full-range electrostatic loudspeaker, designed by Peter Walker and David Williamson, based on Edward W. Kelloggs patent from 19349 Roberto Magalotti - Augusto Sarti
  10. 10. Loudspeakers today •  Permanent magnets have replaced the field coil §  AlNiCo (40) §  Ferrites (50) §  Rare Earth (90) •  Voice coils are designed to handle the large electrical power supplied from modern amplifiers •  Finite Element Analysis is extensively used in all aspects of loudspeaker design (acoustics, thermodynamics, electromagnetism,...) •  Digital Signal Processing is widely used in loudspeaker system set-up and management10 Roberto Magalotti - Augusto Sarti
  11. 11. Directivity in acoustics •  Definition: radiation pattern in the far field with respect to the source(s) •  Far field: the radiation pattern no longer changes with the distance §  Several wavelengths form the source §  Several times the size of the source11 Roberto Magalotti - Augusto Sarti
  12. 12. Specifying directivity 0° 6 330° 0 30° -6 -12 -18 10FCX64 300° 60° -24 -30 500 Hz -36 Woofer 1 kHz -42 270° -48 90° 2 kHz 4 kHz Driver 8 kHz 240° 120° 16 kHz 210° 150° 180°12 Roberto Magalotti - Augusto Sarti
  13. 13. Specifying directivity13 Roberto Magalotti - Augusto Sarti
  14. 14. Specifying directivity14 Roberto Magalotti - Augusto Sarti
  15. 15. Piston in an infinite baffle15 Roberto Magalotti - Augusto Sarti
  16. 16. Piston at the end of a long tube16 Roberto Magalotti - Augusto Sarti
  17. 17. Unbaffled piston17 Roberto Magalotti - Augusto Sarti
  18. 18. Curved source (horn)18 Roberto Magalotti - Augusto Sarti
  19. 19. Directivity shaping with more sources: uniform linear array19 Roberto Magalotti - Augusto Sarti
  20. 20. Directivity shaping with more sources: tapered linear array20 Roberto Magalotti - Augusto Sarti
  21. 21. Directivity shaping with more sources: linear array with delays (beam steering)21 Roberto Magalotti - Augusto Sarti
  22. 22. Line arrays in live audio systems Grateful Dead “Wall of Sound”, 197422 Roberto Magalotti - Augusto Sarti
  23. 23. Line arrays in live audio systems Point source system Line array system23 Roberto Magalotti - Augusto Sarti
  24. 24. Line arrays, early example: Parkin – Taylor 195224 Roberto Magalotti - Augusto Sarti
  25. 25. Line arrays, early example: Parkin – Taylor 195225 Roberto Magalotti - Augusto Sarti
  26. 26. Line arrays, early example: Parkin – Taylor 195226 Roberto Magalotti - Augusto Sarti
  27. 27. Line arrays: V-DOSC by L-Acoustics, 199227 Roberto Magalotti - Augusto Sarti
  28. 28. Line arrays: V-DOSC by L-Acoustics, 199228 Roberto Magalotti - Augusto Sarti
  29. 29. Contemporary line arrays: J-shape29 Roberto Magalotti - Augusto Sarti
  30. 30. Contemporary line arrays: MLA by Martin Audio, 201030 Roberto Magalotti - Augusto Sarti
  31. 31. Contemporary line arrays: MLA by Martin Audio, 2010 DISPLAY 2 rendering software31 Roberto Magalotti - Augusto Sarti
  32. 32. Cardioid subwoofers: principle32 Roberto Magalotti - Augusto Sarti
  33. 33. Cardioid subwoofers: in practice33 Roberto Magalotti - Augusto Sarti
  34. 34. WHAT PROCESSING CAN DO Roberto Magalotti - Augusto Sarti
  35. 35. Perceptual cues for 3D audio Interaural Time/Level Difference35 Roberto Magalotti - Augusto Sarti
  36. 36. Perceptual cues for 3D audio Head Related Transfer Function36 Roberto Magalotti - Augusto Sarti
  37. 37. HRTF37 Roberto Magalotti - Augusto Sarti
  38. 38. Multi-channel audio planar rendering (ITD only)38 Roberto Magalotti - Augusto Sarti
  39. 39. Multi-channel audio vector rendering (ITD only)39 Roberto Magalotti - Augusto Sarti
  40. 40. Beyond ITDBinaural RenderingWavefield Rendering Roberto Magalotti - Augusto Sarti
  41. 41. Wavefield synthesis Huygens’ principle (1690) The wavefield produced by a primary source Ψ can be reconstructed using a distribution of secondary sources41 Roberto Magalotti - Augusto Sarti
  42. 42. Wavefield Synthesis example of focused source42 Roberto Magalotti - Augusto Sarti
  43. 43. Limits•  Large number of speakers•  Hard to go beyond planar rendering•  Invasive installation Roberto Magalotti - Augusto Sarti
  44. 44. From 2D to 3D…•  Large number of speakers•  Hard to go beyond planar rendering•  Invasive installation HoloPlot ModuleMatrix (Advanced Acoustic, Potsdam, Germany) Roberto Magalotti - Augusto Sarti
  45. 45. DT solution to reduce invasivity…45 Roberto Magalotti - Augusto Sarti
  46. 46. Ambisonics fundamentals Ø  Spherical Harmonic Decomposition : Fourier-Bessel series r ∞ p(r ) = ∑ j m jm (kr ) ∑ BmnYmn (θ , δ ) σ σ m =0 0≤ n≤ m,σ =±1 Spherical Harmonic functions: o  Sound field represented by coefficients Bmnσ o  = Spherical Harmonic component ó “Ambisonic Signals” o  ópressure field spatial derivatives of successive orders m o  Around a reference point = listener point of view Spherical Bessel Functions: Intrinsic quality of representation Using components Bmnσ up to a limited order (m≤M) Angular resolution ó radial expansion % wave length46 Roberto Magalotti - Augusto Sarti
  47. 47. Ambisonics rendering Wavefield as a linear combination of (a basis of) spherical harmonic functions47 Roberto Magalotti - Augusto Sarti
  48. 48. Ambisonics rendering Wavefield approximation as the order increases48 Roberto Magalotti - Augusto Sarti
  49. 49. Ambisonics dome in PoliMI49 Roberto Magalotti - Augusto Sarti
  50. 50. Commercial ambisonics installations50 Roberto Magalotti - Augusto Sarti
  51. 51. Commercial ambisonics installations Roberto Magalotti - Augusto Sarti
  52. 52. High-order speakers Adrian Freed, Peter Kassakian, David Wessel (CNMAT) Class-D embedded amplifiers §  Embedded ethernet and DSP Roberto Magalotti - Augusto Sarti
  53. 53. Soundfield sythesis: goals • Render  a  virtual  acous0c  source  using  a  loudspeaker  array   • Render  the  acous0cs  of  a  virtual  environment   • Compensate  for  the  early  reflec0ons  of  the  environment  in  which  the   loudspeaker  array  is  opera0ng  (“room  compensa0on”)   • Exploit  the  early  reflec0ons  of  the  real  environment,  e.g.    for  a  virtual  home   theater  system  53 Roberto Magalotti - Augusto Sarti
  54. 54. Rendering virtual acoustic sources Beamshaping   Goal:   •  Rendering  of  a  virtual  source  along  with  its  radia0on  paDern  in  a  listening  region,  by   means  of  a  loudspeaker  array   •  Focus  on  direc0onal  sources,  modeled  as  beams   •  Need  to  control:   •  Source  posi0on   •  Direc0on  of  emission   •  Beam  aperture   loudspeakers   virtual   source   listening  region  54 Roberto Magalotti - Augusto Sarti
  55. 55. Virtual  environment  rendering   Wave  field  modeled  as  the  superposi0on  of   elementary  beams  (geometrical  acous0cs)   Use  loudspeakers  for   synthesizing  elementary   beams  55 Roberto Magalotti - Augusto Sarti
  56. 56. Virtual  environment  rendering   •  Image  sources  are  suitable  only  in   simple  convex  environments   •  Visibility  tests  are  very  0me  demanding   •  A  convenient  solu0on  is  beam  tracing,   which  compute  visibility  very  efficiently  56 Roberto Magalotti - Augusto Sarti
  57. 57. Virtual  environment  rendering   Examples              NMSE  (%):    500  Hz    à  7.4  %   1000  Hz  à  7.9  %              NMSE  (%):    500  Hz    à  5.1  %   1000  Hz  à  5.3  %  57 Roberto Magalotti - Augusto Sarti
  58. 58. Virtual environment rendering in reverberant rooms •  Loudspeakers  operate  in  an  arbitrary  reverberant  room   •  Image  loudspeakers  determined  through  beam-­‐tracing   •  Room  compensa0on  enables  a  free-­‐field  behaviour  of  the   beam  shaping   •  Design  of  a  virtual  environment  to  be  rendered…   •  …  and  rendering  through  superposi0on  of  beams  58 Roberto Magalotti - Augusto Sarti
  59. 59. Environment-­‐aware  virtual  environment  rendering     Free-­‐field  wf   Non-­‐compensated   Room-­‐compensated   Desired  wave  field   rendering   wf  rendering   wf  rendering  59 Roberto Magalotti - Augusto Sarti
  60. 60. Exploi5ng  the  environment image  array   image  array   (first  order)   (first  order)   …  is  it  possible  to  think  at  the   environment  as  an  “augmented”   rendering  system?   IDEA:  use  the  walls  (i.e.,  image   loudspeakers)  to  increase  the  array   Applica0on:  simula0on  of  a  5.1   surround  system  [Canclini2012]   image  array   image  array   (second  order)   (second  order)  60 Roberto Magalotti - Augusto Sarti
  61. 61. Exploiting the environment Environment-­‐aware   What  about  undesired  reflec0ons?     virtual  5.1  surround   Desired  response   Actual  response   L R RL   RR   C We  can  introduce,  again,  room   compensa0on  (slightly  modified):   G des = G roomC ˆ C = (GT roomGT room ) −1 GT roomG listening  area   des Compensated   loudspeaker  gains   ˆ h comp = Ch ff61 Roberto Magalotti - Augusto Sarti
  62. 62. Exploiting the environment Example:  reproduc0on  of  the  rear-­‐right  channel   Desired   Non-­‐compensated   Room-­‐compensated   RR   listening  area  62 Roberto Magalotti - Augusto Sarti
  63. 63. Exploiting the environment63 Roberto Magalotti - Augusto Sarti
  64. 64. Technological challenges •  Pervasive but non-invasive audio •  Immersive experience •  Contained within the environment •  Acoustic displays should not “take over” but should seamlessly integrate with the surroundings •  Design constraints •  slim, compact, …in the wrong place •  High quality expectations64 Roberto Magalotti - Augusto Sarti
  65. 65. Professional-grade solutions65 Roberto Magalotti - Augusto Sarti
  66. 66. Consumer-oriented solutions MEMS loudspeakers66 Roberto Magalotti - Augusto Sarti
  67. 67. 67 Roberto Magalotti - Augusto Sarti
  68. 68. Lightness “La seconda rivoluzione industriale non si presenta come la prima con immagini schiaccianti quali presse di laminatoi o colate dacciaio, ma come i bit di un flusso dinformazione che corre sui circuiti sotto forma di impulsi elettronici. Le macchine di ferro ci sono sempre, ma obbediscono ai bit senza peso.”68 Roberto Magalotti - Augusto Sarti
  69. 69. Quickness “Sogno immense cosmologie, saghe ed epopee racchiuse nelle dimensioni di un epigramma. Nei tempi sempre più congestionati che ci attendono, il bisogno di letteratura dovrà puntare sulla massima concentrazione della poesia e del pensiero.” •  IPAL (Integrated Powered Adaptive Loudspeaker) §  Virtual Parameter §  Direct Pressure Control §  Processing Time: 10 µs69 Roberto Magalotti - Augusto Sarti
  70. 70. Exactitude “…il giusto uso del linguaggio per me è quello che permette di avvicinarsi alle cose (presenti o assenti) con discrezione e attenzione e cautela, col rispetto di ciò che le cose (presenti o assenti) comunicano senza parole.”70 Roberto Magalotti - Augusto Sarti
  71. 71. Exactitude “…il giusto uso del linguaggio per me è quello che permette di avvicinarsi alle cose (presenti o assenti) con discrezione e attenzione e cautela, col rispetto di ciò che le cose (presenti o assenti) comunicano senza parole.”71 Roberto Magalotti - Augusto Sarti
  72. 72. Visibility “La mente del poeta e, in qualche momento decisivo, la mente dello scienziato, funzionano secondo un proceimento di associazioni di immagine che è il sistema più veloce di collegare e scegliere tra le infinite forme del possibile e dell’impossibile.”72 Roberto Magalotti - Augusto Sarti
  73. 73. Multiplicity “Ogni vita è un’enciclopedia, una biblioteca, un inventario di oggetti, un campionario di stili, dove tutto può essere continuamente rimescolato e riordinato in tutti i modi possibili.” •  Home systems §  From 2-ch stereo... §  ...to multichannel and sound bars •  Cinema Sound §  From 5.1, 7.1, 10.1, 22.2.... §  ...to 3D Sound (Dolby Atmos)73 Roberto Magalotti - Augusto Sarti

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