Audio rendering

Development of an outdoor auralisation prototype with 3D sound reproduction Erlend Magnus Viggen, Audun Solvang, Jakob Vennerød, Herold Olsen {ErlendMagnus.Viggen, Audun.Solvang, Jakob.Vennerod, Herold.Olsen}@sintef.no

Acoustics Research Centre, SINTEF ICT, Trondheim, Norway

Source sound

Sound processing

Propagation

Recording method

Input

Nord2000 model

 Recorded near-field on vehicle

 Source signal at constant speed

 Semi-analytical modelling

 Microphones in front and on back

 Sound paths from propagation model

 Detailed treatment of terrain effects

 Recorded at constant speeds:

 Normally used for noise mapping Processing

 30, 50, 80 km/h

 Performed for each sound path type

 Signal unaffected by propagation or

 Each reflection, diffraction, direct

Doppler shift

 Source signal Doppler shifted accor-

Computation

 Split road source into points  Determine sound paths from each source point to listener

ding to path length evolution

 Direct, reflected, and diffracted

 Resampling by linear interpolation

 Find reflections by beam-tracing

 Shifted signals filtered frame-by-frame according to vehicle position

 Compute 1/3 oct.ave band filters along each path using Nord2000

 Store path’s filter, incoming angles, length, type Extrapolation

3D audio representation

 Not all source points are computed  In some, sound paths are extrapolated

Input

from neighbouring computed points

 Processed source sound for each sound path  Incoming angle for each sound path Spherical harmonics transform

 Treat incoming sound paths as plane waves  Each plane wave is represented with spherical harmonics of order N = 4

 The plane waves are combined to a (N+1) -channel Ambisonics format 2

 The Ambisonics representation can be decoded to different formats and rendered

Audio rendering

Mono

VAD Virtual Auditory Display

Main references 

 Headphones with head tracking  Head tracker updates rotation



matrix frame-by-frame

Stereo

 Spherical harmonics-based HRTFs  High-frequency phase correction for



interaural level differences 

Surround

B. Plovsing, ”Nord2000: Comprehensive outdoor sound propagation model. Part 1.” AV 1849/00, DELTA, 2006. M. A. Poletti, “Three-dimensional surround sound systems based on spherical harmonics,” Journal of the Audio Engineering Society, vol. 53, no. 11, pp. 1004–1025, 2005 J. Vennerød, Binaural reproduction of higher order Ambisonics: A real-time implementation and perceptual improvements, Master’s thesis, NTNU, 2014. J. Forssén, T. Kaczmarek, J. Alvarsson, P. Lund, M. E. Nilsson, ”Auralization of traffic noise within the LISTEN project—preliminary results for passenger car pass-by,” in Euronoise 2009, Edinburgh, Scotland, 2009.