1 Real Time Walkthrough Auralization - the first year from static to dynamic auralization properties and limitations model and receiver grid examples current and future options applications and summary B.-I. DalenbäckCATT M. StrömbergValeo Graphics GothenburgSweden

2 From static to dynamic auralization: 1/6 traditionally, starting around 20 years ago, auralizations have been static: fixed listening positions with fixed head directions. a single static, typically binaural, room impulse response (FIR) is convolved with anechoic sound schematic representation of a static FIR (one head direction): L R time lateearlydirect

3 From static to dynamic auralization: 2/6 a head-tracked binaural early part FIR with a static late part, medium calculation time, fairly memory consuming: L R time lateearlydirect Many early part FIRs corresponding to many head directions A single late part FIR corresponding to one head direction

4 From static to dynamic auralization: 3/6 a head-tracked full-length binaural FIR, long calculation, very memory consuming: L R time lateearlydirect Many full-length FIRs corresponding to many head directions, still just a fixed position

5 From static to dynamic auralization: 4/6 the solution: full-length B-format FIRs, short calculation, not memory consuming: W time lateearlydirect X A single full-length B-format FIR, rotation performed afterwards. YZ L R Binaural decode Each head direction created when needed

6 From static to dynamic auralization: 5/6 CATT-Walker™, putting it all together with many positions, rotating and interpolating while convolving Pre-processing

7 From static to dynamic auralization: 6/6 Real time processing details

8 Properties and limitations the real time part of the process is independent of room complexity (3 sec church “=“ 3 sec shoebox) the prediction and post-processing methods are exactly the same as for static auralization requires a high receiver density where the IR is expected to change fast with movement or head direction

9 Model and receiver grid examples : 1/4 A church walkthrough, 80 receivers, plan view

10 Model and receiver grid examples : 2/4 The church walkthrough, 3D view

11 Model and receiver grid examples : 3/4 The church walkthrough, CATT-Walker™ view

12 Model and receiver grid examples : 4/4 A smaller room walkthrough, 3D model view

13 Current options : 1/2  multiple source simulation at no extra CPU cost (assumes that sound input is common for all sources such as in a PA system)  choice of HRTFs for the binaural decode  choice of headphone eq. for the binaural decode  variable walking speed  optional TCP/IP control via the Walker Steer API  optional trade-off for use with slower PCs (latency and/or horizontal only i.e. based on WXY)

14 Current options : 2/2 Optional grid and WXYZ FIR view

15 Future options : 1/2  detailed models with textured graphics imported from programs such as 3ds max  head-tracking at no extra CPU cost (not crucial in front of a PC screen)  multiple independent sources (higher CPU demand)  Doppler effects (difficult with FIR interpolation, not crucial for room acoustics)  direct B-format output for external decoding to any loudspeaker array (lower CPU demand)

16 Future options : 2/2  ambisonic output for direct loudspeaker replay (lower CPU demand)  use of measured instead of predicted B-format FIRs (can be measured by a Soundfield microphone)  use of 2 nd order B-format FIRs (higher CPU demand, not crucial for a binaural down-mix)

17 Applications  everyday use (processing only longer due to a higher number of receivers)  presentations to clients  presentations in architecture competitions  research projects exploring the possibility to control via TCP/IP. Two example EC-projects:  “POEMS” at Chalmers University, Gothenburg  “Wayfinding” at LIMSI, Paris

18 Summary  a technique for real time walkthrough auralization has been described:  based on B-format FIRs and binaural downmix  is in itself general and can as well be based on measured responses  no special shortcuts made for the real time option  future improvements of prediction and auralization methods will directly carry over to the walkthrough auralization