BPC: Art and Computation – Summer 2007BPC: Art and Computation – Summer 2007

Digital Media - AudioDigital Media - Audio

Glenn Bresnahan

glenn@bu.edu

BPC: Art and Computation – Summer 2007 2

OverviewOverview

Principles and properties of sound and perception – Lessons 5.a & 5.b - 1 class each

• Glenn Bresnahan, Robert Putnam

– Lectures & demonstrations Sound recording and digital editing

– Lesson 6 - 3 classes• Manny Rettinger

– Studio and field work, instruction+lab

BPC: Art and Computation – Summer 2007 3

SynopsisSynopsis

Physical properties Mathematical properties of sine waves

Representation of functions as graphs of sound Characteristics of real sounds Analog and digital representation and

recording of sound Field and studio recording techniques and

equipment Digital audio manipulation and editing

BPC: Art and Computation – Summer 2007 4

Digital Audio: Sound and Hearing (5.a)Digital Audio: Sound and Hearing (5.a)

Objectives– Understanding of the basics physics of

sound• Understanding the fundamentals of waves

– Mathematically– Physical properties of sound waves– Composition of complex waves from sine waves

• Representation and transductions of signals

– Biophysics of human hearing

BPC: Art and Computation – Summer 2007 5

Sound wave conceptsSound wave concepts

Mathematical properties of (sine) waves– Amplitude, wavelength, frequency, period and speed– Representation: function graphs/plots

Principles of sound– Vibrations & resonance– Physical properties of sound (frequency, speed, sound

pressure levels) Real sounds

– Absorption and reflection (reverberation)– Compound frequencies

Signal transduction – Converting between SPL and current

BPC: Art and Computation – Summer 2007 6

Sound waves approachSound waves approach

Analogies to cyclical phenomena – Waves in water, moon phases, sun

rise/set, tides

BPC: Art and Computation – Summer 2007 7

Moon phasesMoon phases

Moon Phase

0%

25%

50%

75%

100%

Date

Per

cen

tag

e V

isib

le (

ph

ase)

BPC: Art and Computation – Summer 2007 8

Cause of tidesCause of tides

Gravity from moon and sun

365 days

27.3 days (29.5 days)

New moon

Full moon

1 day

BPC: Art and Computation – Summer 2007 9

Sunrise and sunsetSunrise and sunset

Sunrise - Sunset Times

0.00

4.00

8.00

12.00

16.00

20.00

24.00

Date

Hour

of D

ay Sunrise Time

Sunset Time

Daylight Hours

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

Date

Ho

urs

of D

aylig

ht

solstice

solstice

BPC: Art and Computation – Summer 2007 10

Sound and vibrationSound and vibration

Demonstration with real instruments

BPC: Art and Computation – Summer 2007 11

Transverse waves in time and spaceTransverse waves in time and space

string

Energy(pluck)

vibration

WaveWaveAir pressure level

BPC: Art and Computation – Summer 2007 12

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

BPC: Art and Computation – Summer 2007 13

Properties of sound – real soundsProperties of sound – real sounds

BPC: Art and Computation – Summer 2007 14

How do we hear?How do we hear?

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

BPC: Art and Computation – Summer 2007 15

Anatomy of the earAnatomy of the ear

BPC: Art and Computation – Summer 2007 16

Haircells and neural firingsHaircells and neural firings

BPC: Art and Computation – Summer 2007 17

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)

BPC: Art and Computation – Summer 2007 18

Lecture MaterialsLecture Materials

Digital Audio Parts 1 & 2:

http://scv.bu.edu/BPC/http://scv.bu.edu/BPC/MaterialsFall06/lectures/BPC-Class-MaterialsFall06/lectures/BPC-Class-DigitalMedia-Audio.pptDigitalMedia-Audio.ppt