Transcript Overview - UCL Computer Science

Audio Systems
Survey of Methods for Modelling
Sound Propagation in
Interactive Virtual Environments
Ben Tagger
Andriana Machaira
Overview Part 1

Audio Systems and Virtual Environments
 Basics of Real & VR World Acoustics
 Basics of the Human Hearing
 Auralization
 Room Effects
Overview Part 2

Some Basic Sound Theory
 Characteristics of Sound
 Methods of simulating the propagation of
Sound through an Environment

Spatialisation Demo
The need of audio in VR

Additional channel of communication
 Formation of spatial information
 Localisation of objects
 Data-driven sound
 Simulation of ‘coctail party effect’
 Sound enhances the presence in the VR
Basics of Real World Acoustics

The sound source
→ Object that emits sound waves

The acoustic environment
→ absorbtion, reflection, refraction
and diffraction of sound waves

The listener
→ From the arriving waves the listener extract
information about the sound sources and the
environment.
Basics of VR World Acoustics

The auditory actor
→Entity emitting sounds through its interface.

The auditory space
→The environment that has to be modeled. An auditory
space object models the geometry of the enclosures in
the world.

The listener
Basics of Human Hearing
Interaural
intensity difference (IID)
→ a sound is louder at the ear that it is closer to
Interaural
time difference (ITD).
→ a sound will arrive earlier at one ear than the other.

Ear pinna
→ key to accurately localizing sounds in space for
wavelengths in the centimeter range or smaller.
Basics of Human Hearing
acoustic transmission pathway into the ear [2]
Head Related Transfer Function
HRTF
HRTF representation [2]
3D interactive Sound System
Sounds are projected
→ in all three dimensions
→ in real-time and interactive rates
→ with the less coloring (tonal changes)
introduced by processing
Auralization.

Auralization is the process of rendering audio
data by digital means to achieve a 3D sound
space.

Principle → Binaural human hearing
 Extract information about the location
of sound sources.
Auralization Processing Pipeline
Basic Auralization Pipeline [4]
Modeling sound propagation
Sound propagation paths from a source (A) to a receiver (R) [4]
Part II Overview

Some Basic Sound Theory
 Characteristics of Sound
 Methods of simulating the propagation of
Sound through an Environment
• Numerical Solutions
• High Frequency Approximations
• Perceptually-based Statistical Models

Spatialisation Demo
Basic Sound Theory

“No one can hear you scream in Space.”

Hit a Tuning fork
 Tuning fork vibrates and hits the air molecules next to
it
 These air molecules hit the ones next to them
 And so on…

Doesn’t work in a vacuum.
Characteristics of Sound

Wavelength
 Speed
 Dynamic Range
 Latency and Update Rate
Wavelength

Wavelengths range - between 0.02 and 17 meters (20 KHz
and 20 Hz respectively)

Reflections are largely specular for large flat surfaces (i.e.,
walls)
 Diffraction of sound occurs around obstacles of the same size
as the wavelength (i.e., tables)
 Small objects have little effect on the sound field (for all but
the highest wavelengths.




Speed
343 MSec-1
Far slower than light
Propagation delays are perceptible to humans.
Sound arrives at the receiver at different times
Dynamic Range/
Latency & Update Rate

Sensitivity of the Human Ear
 The effects of late sound reverberation are much
more significant than for illumination

Timing requirements
 System latency and update rates can have a
significant impact on perceived quality of the
environment.
Some Approaches

Computational methods for simulating the
propagation of sound through an environment.
• Numerical Solutions to Wave Equations
• High Frequency approximation based on geometric
propagation paths
• Perceptually-based statistical models
Numerical Solutions – Finite and
Boundary Element Methods
Boundary/Finite Element
Methods

Subdivide space into elements

Elements are small compared to
a wavelength

Each element provides a linear
equation

Equations are solved with large
amounts of Maths

The acoustic field is calculated
at various points of interest.
Mental Image
Where am I?
Sounds
Magic Box of
Maths
Elements
Your
Sound
Geometric Methods

Model acoustic effects with computations based on
ray theory.

Assume that sound wavelengths are significantly
smaller than the size of obstacles.

Algorithm finds ray paths along which a sound can
travel.

Mathematical models are used to approximate filters.
Propagation Paths
Artificial Reverberation Models
Spatialisation Demo
References
[1] http://www.acoustics.hut.fi/research/aurilization.html
[2] http://www.headwize.com/tech/sibbald_tech.htm
[3] http://alumnus.caltech.edu/~franko/thesis/Chapter1.html
[4] Survey of Methods for modeling Sound Propagation in
interactive Virtual Environment Systems, T. Funkhouser,
N. Tsingos, J.-M. Jot (2004), accepted for publication in
Presence, 2004