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BPC: Art and Computation – Fall BPC: Art and Computation – Fall 2006 2006 Digital media I: Audio Digital media I: Audio Glenn Bresnahan Robert Putnam [email protected] [email protected]

BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam [email protected]@bu.edu [email protected]

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Page 1: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006BPC: Art and Computation – Fall 2006

Digital media I: AudioDigital media I: Audio

Glenn Bresnahan Robert Putnam

[email protected] [email protected]

Page 2: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 2

OutlineOutline

Part I (Glenn)

– What is sound?– How do we hear?

Part II (Robert)

– Qualities of sound– Sound reproduction

• analog v. digital

– Sound in VR

Page 3: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 3

Waves revisitedWaves revisited

Page 4: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 4

Waves – (non)artistic renderingWaves – (non)artistic rendering

Page 5: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 5

Wave propertiesWave properties

How might we describe waves?

Page 6: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 6

Wave propertiesWave properties

How might we describe waves?– Height– Time between waves– Speed of the wave

Page 7: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 7

Shoals and tidesShoals and tides

Page 8: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 8

Tide tablesTide tables

Page 9: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 9

Cause of tidesCause of tides

Gravity from moon and sun

365 days

27.3 days (29.5 days)

New moon

Full moon

1 day

Page 10: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 10

Phases of the moonPhases of the moon

Moon phases:New moonWaxing

crescentFirst quarterWaxing gibbousFull moonWaning gibbousLast quarterNew moon

Page 11: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 11

Moon phasesMoon phases

Moon Phase

0%

25%

50%

75%

100%

Date

Per

cen

tag

e V

isib

le (

ph

ase)

Page 12: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 12

Sunrise and sunsetSunrise and sunset

Sunrise - Sunset Times

0.00

4.00

8.00

12.00

16.00

20.00

24.00

Date

Ho

ur

of

Day

Sunrise Time

Sunset Time

Page 13: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 13

Sunrise and sunsetSunrise and sunset

Daylight Hours

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

Date

Ho

urs

of

Da

ylig

ht solstice

solstice

Page 14: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 14

Waves – sine wavesWaves – sine waves

Sine wave is the fundamental wave

Sine Wave

-1.5

-1

-0.5

0

0.5

1

1.5

Page 15: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 15

Waves – propertiesWaves – properties

Sine Wave

-1.5

-1

-0.5

0

0.5

1

1.5

Amplitude

Wavelength (distance)

Page 16: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 16

Waves in motion – propertiesWaves in motion – properties

Sine Wave

-1.5

-1

-0.5

0

0.5

1

1.5

Period (time for one cycle)

TimeTime 11 22Frequency cycles per time interval

Page 17: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 17

What is sound?What is sound?

Examples

Page 18: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 18

What is sound – vibrationWhat is sound – vibration

Striking an object will cause it to vibrateThe vibration is a sine wave Objects have a natural vibration frequency

– Resonance frequency– Frequency depends on type of material,

thickness, length/size, tension– May have multiple vibrating frequencies

The pitch depends on the frequency Loudness (amplitude) depends on size of the

object

Page 19: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 19

What is sound – vibrations moves airWhat is sound – vibrations moves air

string

Energy(pluck)

vibration

WaveWaveAir pressure level

Page 20: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 20

Properties of soundProperties of sound

Pitch is perception of frequency Frequency is measured in cycles per second

(cps)– Hertz (Hz) = cycles per second– The A above middle C is 440 Hz.– Humans hear appox. 20-20,000 Hz

Sound travels at approx. 1100 feet/second– Speed depends on pressure and temperature– Approx. 750 miles/hour– Approx. 1 mile every 4.8 seconds

Perceived loudness depends on pressure level– Sound pressure is measured in (micro)pascals (20uPa)– Loudness is usually expressed in decibels (dB)

Page 21: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 21

Real WavesReal Waves

Page 22: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 22

Properties of soundProperties of sound

Real sounds are far more complex than simple sine waves– Objects produce vibrations at multiple

frequencies– Sound waves interact with other objects

• Waves bounce (reflect) off surface – Reverberation/echo

• Wave are absorbed by materials

– Sound waves interact with each other

Page 23: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 23

Combinations of wavesCombinations of waves

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

1 26 51 76 101 126

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

1 26 51 76 101 126

Page 24: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 24

Properties of sound – real soundsProperties of sound – real sounds

Page 25: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 25

Electrification of soundElectrification of sound

Microphones– Convert pressure levels into electrical signals

(voltages) Guitar pickups

– Converts string vibration to voltages• The pickup contains a magnet and a coil• The vibrating metal strings alter the magnetic field

and induce a voltage in the coil

Loud speakers convert an electrical signal back into air pressure

Page 26: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 26

How do we hear?How do we hear?

Sound waves move through the air from the sound source to the ear

Page 27: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 27

Anatomy of the earAnatomy of the ear

Page 28: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 28

Anatomy of the ear - outerAnatomy of the ear - outer

Divided into three principal sections– Outer ear– Middle ear– Inner ear

Outer ear– External ear, aka pinna– Ear canal– Outer ear funnels the ear have to the

eardrum

Page 29: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 29

Anatomy of the ear - middleAnatomy of the ear - middle

Middle ear– Eardrum– Set of 3 ear bones

• the 3 bones are rigid

– Act as a mechanical amplifier

– The 3rd bone, stapes, induces a vibration into the inner ear, i.e. the cochlea

Page 30: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 30

Anatomy of the ear - innerAnatomy of the ear - inner

Inner ear / cochleaWhere the real work

is doneCochlea is a spiral

tube and filled with fluid

Stapes causes a wave to pass through the fluid

Page 31: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 31

Anatomy of the ear - innerAnatomy of the ear - inner

Cochlea is a spiral tube lined with hair cells on a membrane (~15K HCs)

Hairs vary in length and thickness along the tube

Hairs resonate at different frequencies– High freq on near end,

low at far end

Page 32: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 32

Anatomy of the ear - innerAnatomy of the ear - inner

Page 33: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 33

Anatomy of the ear - innerAnatomy of the ear - inner

Hair cells are connected to the auditory nerve cells

The vibrations excite the nerve cells and cause them to fire (electrical signal)

A series of nerve cells pass the signal to brain

Page 34: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 34

Binaural hearing - why two ears?Binaural hearing - why two ears?

Two ears, so we can identify locations of sounds– Time difference– Intensity difference– Sound color difference (caused by

movement of sound around head and shoulders)

Page 35: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 35

Sound localization – pinnaSound localization – pinna

front

back Sound waves interact with

the asymmetric Pinna The effect on the sound

varies with the direction Up/down, back/front waves

result in different sounds entering ear canal

Page 36: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 36

Digital media I: part IIDigital media I: part II

Other qualities of sound: pitch, timbre, “noise”, envelope

Sound reproduction: analog v. digitalSound in VR

Page 37: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 37

What is pitch?What is pitch?

Our perception of the highness or lowness of a tone.

Closely related to frequency When frequency doubles, pitch rises by an

“octave” Examples But, what happens when there’s more

than one frequency in a sound?

Page 38: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 38

Review: modes of vibration of a Review: modes of vibration of a stringstring

Fundamental

[e.g., 110 Hz]

2nd harmonic

[e.g., 220 Hz]

3rd harmonic

[e.g., 330 Hz]Examples

Page 39: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 39

TimbreTimbre

Sound color, or “timbre” is a quality of sound that derives from the particular combination of frequencies (a.k.a., “harmonics” or “partials”) in a tone.

Two sounds can contain the same harmonics but sound very different because their individual harmonics are of different amplitudes.

Examples

Page 40: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 40

Timbre, continuedTimbre, continued

Easy to demonstrate timbre with human voice

Hum.Slowly open mouth.Hear how the sound color changes

from “dark” to “bright”Example

Page 41: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 41

Timbre, continued.Timbre, continued.

Timbre changes as a wind instrument is played louder or softer.

Example

Page 42: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 42

Unpitched soundsUnpitched sounds

Can use human voice to demonstrate another distinction: pitched versus unpitched sounds

Make “s” soundNo identifiable “pitch”Related to concept of “noise”Examples

Page 43: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 43

ExamplesExamples

Pitched sounds– Birdsong– Flutes– Stringed instruments– Etc.

Examples of unpitched sounds– Certain percussion instruments (cymbals, ratchets, etc.)– Wind, rain, footsteps in snow

Listen now. What do you hear? Frequencies, amplitudes. Pitched, unpitched. External versus internal sources.

Page 44: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 44

Time variation of soundsTime variation of sounds

Most naturally occurring sounds are not static; i.e., they vary over time– Amplitude– Pitch– Timbre

Examples

Page 45: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 45

Sound recording technologiesSound recording technologies

AnalogDigital

Page 46: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 46

Analog recordingAnalog recording

Analog: “device or system that represents changing values as continuously variable physical quantities.”

Example: clock with hour, minute and second hands

Question: what values are changing when we hear sound?

Page 47: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 47

Analog recording technologiesAnalog recording technologies

Phonautograph

Page 48: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 48

Analog recording technologiesAnalog recording technologies

Mechanical: Gramophone, LP record, etc.

Page 49: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 49

Analog recording technologiesAnalog recording technologies

Magnetic: Wire, tape recorder.

Page 50: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 50

Analog recording technologiesAnalog recording technologies

Optical: movie soundtrack.

Page 51: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 51

Analog sound reproductionAnalog sound reproduction

Amplification

Loudspeaker demo

Page 52: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 52

Digital recordingDigital recording

Digital: “device or system that represents changing values as discontinuous, or ‘discrete,’ values.”

Example: clock with number readout.

Page 53: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 53

Digital recordingDigital recording

With digital recording, we do not store a continuous record of the rise and fall of air pressure. We make measurements of the air pressure (or the voltage produced by a microphone) thousands of times per second and store these measurements as numbers.

Page 54: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 54

Digital recordingDigital recording

Analog: continuous waveform

Digital: discrete values

Page 55: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 55

Some buzzwordsSome buzzwords

ADC: analog-to-digital converterDAC: digital-to-analog converterSampling rate: samples/secondWord size: how much storage for

each sampleQuantization: [see next slide]

Page 56: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 56

QuantizationQuantization

Selecting sample value from finite set of numbers.

16 bits = 65,536 choices

20 bits = 1,048,576 choices

Source: http://advisor.matrasi-tls.fr/digital_sampling_index.html

Page 57: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 57

CD audioCD audio

44,100 samples per second.16-bit samples (65536 different

possible values)Frequency range: 0-22KHz.

Page 58: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 58

Some benefits of digital audioSome benefits of digital audio

Easy to edit (visual interface)No noise with additional generationsFlexible signal processing (no

special hardware)Examples (reverb, pitch shift, noise

reduction, etc.)

Page 59: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 59

An aside: MP3 audioAn aside: MP3 audio

CD takes up a lot of space: 3 minute song = 44100*2*2*3*60 = 31752000 B.

MP3 compression results in a factor of 5-10 savings in storage, but lower fidelity (e.g., noisier).

Page 60: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 60

Another aside: MIDIAnother aside: MIDI

Musical Instrument Digital InterfaceA communications scheme for

computers, synthesizers, sequencers, etc.

Suited for popular musicStores Note-On, Note-Off, Velocity,

etc. (i.e., not waveforms)Example

Page 61: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 61

DAFFIE audioDAFFIE audio

Soundserver– Plays sound files associated with

objects– Mixes many simultaneous sounds– Internet telephony support

Page 62: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 62

DAFFIE localizationDAFFIE localization

All sounds are assigned a location in virtual space.

Typically, sounds are associated with visible objects, but “ambient” sound (e.g., wind, nature) is supported too.

Direction and distance are indicated by variations in loudness among the loudspeakers – done automatically by soundserver.

Page 63: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 63

Uses of sound in VRUses of sound in VR

Communication (via telephony)Sound effectsMusic selectionsAmbient audioLive audio (via telephony)Previous projects have involved

controlling synthesizers or musical instruments remotely.

Page 64: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 64

Recording sounds for DAFFIERecording sounds for DAFFIE

Field recording versus studio recording

Record, record, recordRemember that sounds are

combined “in real time” by the soundserver (so no need to put everything in a single file).

Stereo is good.

Page 65: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 65

Recording sounds for DAFFIE, part Recording sounds for DAFFIE, part II.II.Remember that you can change

sounds in various ways– Change pitch/tempo– Use filters to change spectrum– Cut and paste

Page 66: BPC: Art and Computation – Fall 2006 Digital media I: Audio Glenn Bresnahan Robert Putnam glenn@bu.eduglenn@bu.edu putnam@bu.edu

BPC: Art and Computation – Fall 2006 66

DAFFIE demoDAFFIE demo

Demonstrate– Proximity triggering– (Variable) Distance attenuation– Sound localization