fall 2008 introduction & the physics of sound€¦ · fundamentals of acoustics (the physics of...

COSC 6002:Auditory Perception and Virtual Audio

Fall 2008

Professor Bill Kapralos

COSC 6002, Fall 2008, Professor Bill Kapralos

Fall 2008

Introduction & the Physics of SoundMonday, September 8 2008


Overview (1):Administrative Details

Some course preliminaries

Final course project

Obtaining help

Professor specific policies

University specific policies

Course objectives and course content (“roadmap”)

Motivation – The Importance of SoundMotivation

Spatial sound in games and virtual environments

Overview (2):Introduction to the Physics of Sound

Introduction to waves

Categorizing waves

Anatomy of sound

Sound wave properties

Measuring SoundIntroduction

Intensity

Decibels

Sound meters


Fall 2008


Overview (3):Sound Interaction

Acoustical reflection phenomena

Refraction

Diffraction

Differences between sound and light waves

Administrative Details

Course Preliminaries (1):Instructor: Bill Kapralos

Email: [email protected] or [email protected]

Office hours: TBA (probably before or after the lecture)

or by appointment

Recommended TextbookMichael Vorlander. Auralization:Fundamentals of Acoustics, Modelling, Simulation, Algorithms and Acoustic Virtual Reality. Springer Verlag Publishers. 2008. ISBN: 3540488294.


Fall 2008


Course Preliminaries (2):Tentative Grading Scheme (may change):

Mid-Term Exam 20% Date TBAFinal Project 40% Exam periodPresentations 25% As assignedParticipation 15%

Note: These dates are tentative and may change!

Final Course Project (1):Overview

Course will consist of a final project with deliverables (milestones) throughout the semester

Will involve the development of virtual audio application and will consist of the following

The virtual audio application itselfDemo and presentation in front of the classResearch paper describing the developed system

Choosing a topicFlexibility and freedom to explore a topicI can provide suggestions…

Obtaining Help (1):Various Ways to Obtain Help

If you have any course-related issues, take advantage of the opportunity to approach me!

See me in person

Email me


Fall 2008


Obtaining Help (2):Course Website

All course-relevant material and information will be made available via the course website

Announcements, etc.

Check often…

http://faculty.uoit.ca/kapralos/COSC6002/generalInfo.html

Professor Specific Policies (1):Cell Phones OFF!

Please keep your cell phones from ringing during the lecture!

University Specific Policies (1):Academic Integrity and Honesty

Any student found to be involved in plagiarism or cheating will be penalized in accordance to the Department of Computer Science and Engineering Academic Honesty Guidelines

http://www.cse.yorku.ca/admin/coscOnAcadHonesty.html

Suspension from the University and inability to enroll in a course at any university in Canada may be implemented as penalty if a student is found to be guilty of acts of academic misconduct


Fall 2008


University Specific Policies (2):Last Day to Withdraw Without Academic Penalty

Last day to withdraw from this course without receiving a

grade is Friday, November 7 2008.

Professor Specific Policies (3):Missed Mid-Term Exam

Provided valid documentation is provided, a re-make exam will be arranged

In such a situation, you must inform the professor immediately

Professor Specific Policies (4):Lectures

If applicable, “preliminary” lecture notes will be made

available prior to each lecture and “final” lecture notes

will be available after the lecture (final lecture notes may

vary slightly from the preliminary notes)


Fall 2008


Course Objectives (1):Course Description

To be immersed in a virtual environment, the user must be presented with plausible sensory input including auditory cues. A virtual (three-dimensional or spatial) audio display aims to allow the user to perceive the position of a sound source at an arbitrary position in three-dimensional space despite the fact that the generated sound may be emanating from a fixed number of loudspeakers at fixed positions in space or a pair of headphones.

Course Objectives (2):Course Description (cont.)

The foundation of virtual audio rests on the development of technology to present auditory signals to the listener's ears so that these signals are perceptually equivalent to those the listener would receive in the environment being simulated. This directed reading course will examine the human perceptual and technical literature relevant to the modeling and generation of accurate audio displays for virtual environments. Approaches to acoustical environment simulation will be summarized and the advantages and disadvantages of the various approaches will be presented.

Course Objectives (2):Learning Outcomes

Students who successfully complete the course have reliably demonstrated the ability to:

Fundamentals of acoustics (the physics of sound and sound propagation).

Psychoacoustics (human auditory perception).

Auralization (and signal processing for auralization).

Simulation of sound in rooms (acoustical modelling).

3D sound reproduction and virtual reality systems.

Graphics processing unit (GPU) applied to auralization.


Fall 2008


Course Content (“Roadmap”) (1):Overview

Being a reading course, I will not be lecturing in the “traditional” sense

I will provide three introductory lecture to introduce the foundations of human auditory perception and virtual audio

The reminder of the course will involve reading papers, presentations, and discussions

Course Content (“Roadmap”) (2):

Final course project presentations and demonstrations12

Assigned readings, student presentations, and discussion – may inlcude-Advanced psycho-acoustics-Auditory motion perception (and interaction with other cues) -Advanced acoustical modeling (sonel mapping, probabilistic methods..)-GPU and audio/3D sound (2 weeks)-Interaction between audio and other modalities-Loudspeaker-based methods-HRTF dimensionality reduction-Audio for games

4 - 11

Advanced virtual audio generation and open topics (lecture)3

Introduction to psychoacoustics (auditory perception) and virtual audio (lecture).2

Course overview including details regarding the final course project and an introduction to the physics of sound and acoustics (lecture).1

TopicWeek

Motivation:The Importance of Sound


Fall 2008


Motivation (1):Importance of Real World Sounds

Sounds give detailed info of our surroundings

Determine direction and distance to objects

Warn of approaching dangers → particularly important in the “animal kingdom” e.g. predators

Unlike vision, hearing is omni-directional

Can hear in complete darkness!

Can guide the more “finely tuned” visual system

Eases the burden of the visual system

Motivation (2):Sound is an Essential Part of Any Immersive

Environment (VR, Games, etc.)Conveys basic information to the the users

e.g., footsteps in a small room vs. footsteps outside in a large open field

Allows users to orient themselves

Increases situational awareness

Helps increase immersion and hence presence

Can enhance perception of poor video

Can provide a sense of ambience → mood and emotion

Motivation (3):Sound is an Essential Part of

Any Immersive Environment

(VR, Games, etc.) (cont.)Namco’s Pac-man (1980)

“The world’s most popular arcade video game ever”

You can still recollect a “key”sound in this game → sound is more important than you might have thought!


Fall 2008


Spatial Sound in Games and VE (1):Spatial Sound Often Ignored

When present, typically:

Cues are poor and don’t always reflect natural spatial cues → in many games, the only sound cue used is intensity (e.g., lower intensity for a sound source farther away)

“Far field” acoustical model assumed with source at infinity, plane waves and lack of environmental realism (more later…)

Emphasis is typically placed on visual senses

Graphics, stereo vision, etc…

Spatial Sound in Games and VE (2):Spatial Sound Often Ignored (cont.)

Consider the following quote from Wayne Witanen, J. Martin Graetz and Steve Russel in 1962

Creators of SpaceWar! the first computer game

“Although sound support had originally been planned it was never included in the original game in favor for other features that are deemed much cooler and more important…

Although the situation has improved somewhat, unfortunately, sound is, in many situations, still overlooked!

Spatial Sound in Games and VE (3):Fortunately, The Situation is Improving!

Sound is becoming an important part of the “next-generation” video game consoles

XBOX 360 → Multi-channel surround sound output

PS2 → multi-player games that allow players to talk to each other…

If sound wasn’t important, these new consoles would not include specialized audio processors!


Fall 2008


Introduction to thePhysics of Sound

Introduction to Waves (1):What is a Wave ?

A disturbance that travels through a medium, transporting energy from one location to another location

Medium is simply the material through which the disturbance is moving through → can be thought of as a series of interacting particles

Introduction to Waves (2):What is a Wave ?

Waves are every where and we encounter waves on a daily basis

Sound waves, visible light waves, radio waves, microwaves, water waves, sine waves, cosine waves, telephone chord waves, stadium waves, earthquake waves, waves on a string, and slinky waves are just a few of the examples of our daily encounters


Fall 2008


Introduction to Waves (3):What is a Wave ? (cont.)

For many people, the first thought concerning waves

A wave moving across the surface of an ocean, lake, pond or other body of water

The waves are created by some form of a disturbance, such as a rock thrown into the water, a duck shaking its tail in the water or a boat moving through the water

Introduction to Waves (4):Water Waves

The water wave has a crest and a trough and travels from one location to another

One crest is often followed by a second crest which is often followed by a third crest, etc.

Every crest is separated by a trough to create an alternating pattern of crests and troughs

A duck or gull at rest on the surface of the water is observed to bob up-and-down at rather regular time intervals as the wave passes by

Introduction to Waves (5):Water Waves (cont.)

The waves may appear to be plane waves which travel together as a front in a straight-line direction, perhaps towards a sandy shore

Trough

Crest


Fall 2008


Introduction to Waves (6):Water Waves (cont.)

Waves may be circular (spherical) waves which originate from the point where the disturbances occur

Such circular waves travel across the surface of the water in all directions

TroughCrest

Introduction to Waves (7):“Slinky” Waves

Another picture of waves involves the movement of a slinky or similar set of coils

If a slinky is stretched out from end to end, a wave is introduced into the slinky by either vibrating the first coil up and down vertically or back and forth horizontally

Introduction to Waves (8):“Slinky” Waves (cont.)

A wave will subsequently be seen traveling from one end of the slinky to the other

As the wave moves along the slinky, each individual coil is seen to move out of place and then return to its original position

The coils always move in the same direction that the first coil was vibrated

A continued vibration of the first coil results in a continued back and forth motion of the other coils


Fall 2008


Introduction to Waves (9):An Energy Transport Phenomenon

As a disturbance moves through a medium from one particle to its adjacent particle, energy is being transported from one end of the medium to the other

In a slinky wave, a person imparts energy to the first coil by doing work upon it

The first coil receives a large amount of energy which it subsequently transfers to the second coil

When the first coil returns to its original position, it possesses the same amount of energy as it had before it was displaced

Introduction to Waves (10):An Energy Transport Phenomenon (cont.)

As a disturbance moves through a medium from one particle to its adjacent particle… (cont.)

The first coil transferred its energy to the second coil → second coil then has large amount of energy which it subsequently transfers to the third coil

When third coil returns to its original position, it possesses the same amount of energy as it had before it was displaced

The third coil has received the energy of the second coil…

Introduction to Waves (11):An Energy Transport Phenomenon (cont.)

Important

A wave transports energy and not matter!

When considering the slinky, the coils of the slinky return to their original position


Fall 2008


Introduction to Waves (12):Summary

A wave can be described as a disturbance which travels through a medium, transporting energy from one location (its source) to another location without transporting matter

Categorizing Waves (1):Different Types of Waves

Waves come in many shapes and forms

While all waves share some basic characteristics and behaviors, some waves can be distinguished from others based on some very observable (and some non-observable) characteristics.

It is common to categorize waves based on these distinguishing characteristics

Categorizing Waves (2):Different Types of Waves (cont.)

One way to categorize waves is on the basis of the direction of movement of the individual particles of the medium relative to the direction which the waves travel

Categorizing waves on this basis leads to three notable categories

Transverse waves

Longitudinal waves

Surface waves


Fall 2008


Categorizing Waves (3):Transverse Waves

A wave in which particles of the medium move in a direction perpendicular to the direction which the wave moves

Categorizing Waves (4):Longitudinal Waves

A wave in which particles of the medium move in a direction parallel to the direction which the wave moves

Categorizing Waves (5):Surface (Circular) Waves

Particles of the medium undergo a circular motionNeither longitudinal nor transverseIn a surface wave, it is only the particles at the surface of the medium which undergo the circular motion


Fall 2008


Categorizing Waves (6):Mechanical vs. Electromagnetic Waves

Another way to categorize waves is on the basis of the ability (or non-ability) to transmit energy through a vacuum

Categorizing waves on this basis leads to two notable categories

Electromagnetic waves

Mechanical waves

Categorizing Waves (7):Electromagnetic Waves

A wave which is capable of transmitting its energy through a vacuum (e.g., empty space)

Produced by the vibration of electrons within atoms on the sun's surface

Travel through the vacuum of outer space subsequently reaching Earth

Light waves are examples of electromagnetic waves

Categorizing Waves (8):Mechanical Waves

A wave which is not capable of transmitting its energy through a vacuum

Require a medium in order to transport their energy from one location to another

A sound wave is an example of a mechanical wave

Sound waves are incapable of traveling through a vacuum → sound cannot propagate in outer space!


Fall 2008


Anatomy of Sound (1):What Exactly is Sound ?

Mechanical (and longitudinal) wave

Variations in air pressure caused by a physically vibrating object

Guitar string, tuning fork, vocal chords, etc…

Alternating regions of compression and rarefaction of the air (medium) molecules

The vibrating object produces equivalent pulses through a compressible material (medium) typically air

Anatomy of Sound (2):What Exactly is Sound ? (cont.)

Graphical illustration

Sound in air

Regions of compression

Regions of rarefaction

Anatomy of Sound (3):Sound Propagation

As a sound wave moves from the lips of a speaker (or any other vibrating object) to the ear of a listener

Particles of air vibrate back and forth in the same direction and in the opposite direction of energy transportEach individual particle pushes on its neighboring particle so as to push it forwardThe collision of particle #1 with its neighbor serves to restore particle #1 to its original position and displace particle #2 in a forwards direction


Fall 2008


Anatomy of Sound (4):Sound Propagation (cont.)

As a sound wave moves from the lips of a speaker (or any other vibrating object) to the ear of a listener (cont.)

This back and forth motion of particles in the direction of energy transport creates regions within the medium where the particles are pressed together and other regions where the particles are spread apart

Anatomy of Sound (5):What Exactly is Sound ? (cont.)

Animated graphical illustrationSound resulting from tuning fork → metal object consisting of two tines capable of vibrating if struck by a rubber hammer or mallet

Tuning fork

Anatomy of Sound (6):Summary

The medium is simply a series of interconnected and interacting particles

There is an original source of the wave, some vibrating object capable of disturbing the first particle of the medium

Could be the vocal chords of a person, the vibrating string and sound board of a guitar or violin, the vibrating tines of a tuning fork, or the vibrating diaphragm of a radio speaker The sound wave is transported from one location to another by means of the particle interaction


Fall 2008


Anatomy of Sound (7):Summary (cont.)

The medium is typically air but it can be anything

Steel, wood, plastic etc.

Of course the properties and characteristics of the medium will influence the wave

Sound Waves Properties (1):Sine Wave (Tone or Pure Tone)

Simplest type of sound wave

Crest

Trough

Sound Wave Properties (2):Common Characteristics

Amplitude (A)

Maximum displacement from the “mean” (zero position)

Frequency (f)

Number of cycles per second

Number of times per second that the sine wave repeats itself

Measured in Hertz (Hz)


Fall 2008


Sound Wave Properties (3):Common Characteristics

Period (p)

Time required to complete one cycle

Reciprocal of frequency

Phase (φ)

Relative starting time

Important typically only when considering more than one sinusoid

Sound Wave Properties (4):As an Aside

Although sinusoidal sound waves are easy to analyze, they are typically not encountered in our daily lives

The sounds we typically hear are much more complex and typically also not periodic

This is not a problem

As you will discover in the tutorials, any complex sound wave can be decomposed into a number of individual sinusoidal waves → Fourier transform

Sound Wave Properties (5):Speed of Sound

The speed of an object refers to how fast an object is moving and is usually expressed as the distance traveled per unit time of travel

In the case of a wave, speed is the distance traveled by a given point on the wave (such as a crest) in a given interval of time (speed = distance / time)

Example → if the crest of an ocean wave moves a distance of 20 meters in 5 seconds, then the speed of the ocean wave is 4 m/s


Fall 2008


Sound Wave Properties (6):Speed of Sound (cont.)

Sound waves in air travel ~344 meters in 1 second, so the speed of the wave is ~344 m/s

Speed of sound is dependent on the medium

Speed of sound in salt-water → 1500 m/s

Speed of sound in fresh-water → 1435 m/s

Speed of sound is also dependent on the characteristics of the medium

Temperature (to a large degree)

Humidity to some degree, etc.

Differences Between Light & Sound (1):Two fundamental Differences Between

Propagation of Light and Sound Waves

1. Slower propagation speed of sound

2. Attenuation of sound energy by the medium

Additional DifferencesDifferent frequency range

Sound waves are coherent → phase is important!

Differences Between Light & Sound (2):Propagation Speed

Speed of light → 299,792,458m/sPropagation speeds can be ignored and considered instantaneous

Speed of sound → ~344m/sRather slow when compared to light!Can detect (perceive) the propagation delays of sound as it arrives from the sound source to the receiver both directly and indirectly via reflectionsIn fact, time delays between arrival of sound to each ear are a primary sound localization cue


Fall 2008


Differences Between Light & Sound (3):Attenuation by the Medium

Attenuation of light by medium is so small and is ignored by conventional image rendering algorithms

Assume light interacts only with surfaces/objects except in several situations such as light passing through fog, smoke…

Attenuation of sound by medium can’t be ignored as it can be significant and can be perceived

Absorption of higher frequency components of sound varies as a function of distance providing a cue to sound source distance (more next week…)

Measuring Sound

Introduction (1):Energy Carried by a Sound Wave

Recall Sound wave propagation → carried by the disturbance that was originally imparted to the medium by the vibrating object

The amount of energy transferred to the medium is dependent upon the amplitude of vibrations of the vibrating object

If more energy is put into the vibrating object (that is, more work done to displace the object a greater amount from its rest position), then object vibrates with a wider amplitude


Fall 2008


Introduction (2):Energy Carried by a Sound Wave (cont.)

The greater the amplitude of vibration of the object →the more energy to the medium

This causes the air particles to be displaced a greater distance from their rest position

The amplitude of vibration of the particles of the medium is increased → corresponds to an increased amount of energy being carried by the particles

Intensity (1):What is Intensity ?

The amount of energy transported past a given area of the medium per unit of time

The greater the amplitude of vibrations of the particles of the medium → the greater the rate at which energy is transported through it and the more intense that the sound wave is

Intensity is the energy/time/area

Since the energy/time ratio is equivalent to power, intensity is simply the power/area (W/m2)

Intensity (2):What is Intensity ? (cont.)

Humans are equipped with very sensitive ears capable of detecting sound waves of extremely low intensity

The faintest sound which the typical human ear can detect has an intensity of 1×10-12W/m2

Corresponds to a pressure wave where a compression of the particles of the medium increases the air pressure in that compressional region by a mere 0.3 billionths of an atmospheric pressure → corresponds to a sound which will displace particles of air by one-billionth of a cm


Fall 2008


Decibel Scale (1):What is the Decibel Scale ?

Since the range of intensities which the human ear can detect is so large, the scale which is frequently used by physicists to measure intensity is a scale based on multiples of 10

The scale for measuring intensity is the decibelscale (referred to as a logarithmic scale)

Decibel Scale (2):What is the Decibel Scale ? (cont.)

The threshold of hearing (the faintest sound we can hear) is assigned a sound level of 0 decibels (abbreviated 0 dB) → this sound corresponds to an intensity of 1×10-12W/m2

A sound which is 10 times more intense (1×10-11W/m2) is assigned a sound level of 10 dB



Decibel Scale (3):What is the Decibel Scale ? (cont.)

A sound which is 10,000 times more intense (1×10-8W/m2) is assigned a sound level of 40 dB

A sound which is 100,000 times more intense (1×10-7W/m2) is assigned a sound level of 50 dB

An so on…

Decibel scale is based on powers (or multiples) of 10

If one sound is 10x times more intense than another sound → it has a sound level which is 10 more decibels than the less intense sound


Fall 2008


Decibel Scale (4):What is the

Decibel Scale ?

(cont.)Common sounds and their Decibel level

Decibels measures are relative to the TOH (threshold of hearing)

Sound Meters (1):What is a Sound Meter ?

Used to measure sound levels

Sound Interaction


Fall 2008


Acoustical Reflection Phenomena (1):Specular Reflection

Angle of incidence = angle of reflection

θ θ ‘

N

Reflected waveIncident wave

Surfacenormal

IncomingWave-front

ReflectedWave-front

Acoustical Reflection Phenomena (2):Diffuse Reflections

Incident sound reflected in all (or almost all) directions equally as opposed to a single direction

“Scattering” or “dispersion” of sound

Dependent on surface roughness and wavelength

Occurs when roughness of surface is in the order of the wavelength of the incident sound

Acoustical Reflection Phenomena (3):Diffuse Reflection - Graphical Representation

“Rough” Surface

Incident wavefront Reflected waves

(“rays”)


Fall 2008


Refraction (1):What is Refraction ?

Changing of the direction of propagation of a sound wave as it encounters changes in the medium

The two media will have different characteristics leading to different propagation speeds

When considering propagation within a room, refraction can typically be ignored since the characteristics of medium are generally uniform and don’t change

Refraction (2):What is Refraction ? (cont.)

Denser medium -greater sound

velocity

Less dense medium decrease in sound

velocity

A

B

D

C

Wavefront

Boundary between media

with differing characteristics

Diffraction (1):What is Diffraction ?

Bending of sound waves around corners and obstacles

Spreading out of sound waves through small openings

Allows us to hear sounds around corners and barriers

Dependent on both wavelength and obstacle size

Diffraction increases as ratio between wavelength and obstacle size is increased

Diffraction typically greater for lower frequency sounds and when the obstacles are small

When the obstacles are large very few, if any of the waves will be able to bend around the obstacle


Fall 2008


Diffraction (2):What is Diffraction ? (cont.)

Observer

Observer

fall 2008 introduction & the physics of sound€¦ · fundamentals of acoustics (the physics of...

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