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RESEARCH PAPER

ACM SIGGRAPH PROCEEDINGS

Title: Interactive Acoustic Modeling of Complex Environments

Authors: Thomas A. Funkhouser, Ingrid Carlborn, Gary Elko, Gopal Pringali, Mohan Sondhi, Jim West

Presented by: Ng Kae Mun, Bernard

Purpose of Paper: To develop data structures and algorithms to enable interactive simulation of acoustic effects in large 3D environment.

Major Contribution: "Beam tree" – maps the convex pyramidal beam-shaped paths of significant transmission and specular reflection from a point source through 3D space.

Method used: pre-compile and store a spatial data structure that can be used during an interactive session for evaluation of reverberation paths.

Results and Discussion:

1) Beam tree is generated by:

a) Partitioning 3D space into convex polyhedral regions

b) Computing the convex polygonal boundaries between regions

c) Recursively splitting and tracing convex polyhedral beams from a source point through region boundaries (eg. Reflecting beams at opaque boundaries)

2) The pre-computed beam tree data structure can be used to compute specular reflection and transmission paths from a source position to any point in space at interactive rates.

3) The lengths and directions of computed reveration paths may be used to spatialize audio source signals to a receiver moving under interaction control by a user.

4) These data structures and algorithms have been integrated into a system for interactive acoustic modeling. The system takes as input:

a) a set of polygins describing the geometry and acoustic surface properties of the environment, and

b) a set of anchoic audio source signals at fixed locations.

5) It outputs an audio signal auralised according to computed delays, directions and attenuations of the specular reverberation paths from each source to receiver point.

6) The receiver point can be moved interactively by the user allowing real-time exploration of acoustic environments.

SUMMARY:

1) Computer-aided acoustic modeling tools are important for design and simulation of 3D environments.

2) It is also used to provide sound cues to aid understanding, navigation and communication in interactive virtual environment applications, especially updating acoustical simulations at interactive rates.

3) Its primary challenge is computation of reverbation paths from a sound’s source position to a listener’s receiving position.

4) As sound may travel from source to receiver via a multitude of reflection, transmission, and diffraction paths, accurate simulation is extremely compute-intensive.

5) Its current approaches include:

a) Image source methods –

Complexity grows with O(n^r) whereby n = surfaces and r = reflections.

b) Ray-tracing methods –

Prone to sampling error and lots of computation to trace many rays.

6) The solution is using a "beam tree" data structure which is later used during an interactive session for reverberation paths like specular reflection and transmission paths that are used to spatialize audio source signals to a receiver.

7) Together with algorithms, a system for interactive acoustic modeling is created!

Webpage: http://www.cs.princeton.edu/~funk/rsas.html