COSC1078 Introduction to Information Technology Lecture 5 Audio

Lecture 5: Audio Intro to IT

COSC1078 Introduction to Information Technology

Lecture 5

AudioJames Harland

[email protected]


Introduction

James Harland• Email: [email protected]• URL: www.cs.rmit.edu.au/~jah• Phone: 9925 2045• Office: 14.10.1 (Building 14, level 10,

room 1)• Consultation: Mon 4.30-5.30, Thu 11.30-

12.30What is the view like from

my office?


Overview Questions?

Assignment 1

Audio

Questions?

Lecture 4: Images Intro to IT

Introduction to IT1 Introduction 2 Images3 Audio4 Video WebLearnTest 1 5 Binary Representation Assignment 16 Data Storage7 Machine Processing8 Operating Systems WebLearn Test 19 Processes Assignment 210 Internet11 Internet Security WebLearn Test 312 Future of IT Assignment 3, Peer and Self Assessment

Lecture 5: Audio SE Fundamentals

Questions?

How did you spend 6-8 hours on this course last week? This week?


Assessment Process Submit all assignments via Blackboard in the

Learning Hub Assignment 1 due 11.59pm Sunday 1st April Assignment 2 due 11.59pm Sunday 6th May Assignment 3 due 11.59pm Sunday 27th May Late assignments attract a penalty of 10% per

day late, up to a maximum of 50%


Assignment Assignment will be in three parts Overall task is to produce a video Groups of up to 3 Assessed by final video and group blog Part 1: images and audio (end of week 5) Part2: hardware (end of week 9) Part 3: reflection, research (end of week 12)


Assignment 1

Use GIMP (or a similar tool) to perform some manipulations on an image

Use Audacity to perform some manipulations on sound

Use a movie making tool to produce something like (and much better than!) ‘Lord of the Controllers 1 & 2’

Email me your group and its name so that I can set up a blog on the Learning Hub


Assignment 1


Overview 01010100001010101010100110100010101001101001010010100011100010101010100101111001001010…


What is sound?

Vibrations in a medium (air, water, … )

Disturbances in the medium propagate away from the source

Modelled mathematically as waves

Does not travel in a vacuum (``In space, no-one can hear you swear’’ )


Frequency

How many complete cycles within a unit of time

Higher frequency means higher pitch


Sound intensity

How can you measure loudness?

Can measure power/energy/voltage per unit area

Standard unit of comparison is bel or decibel

#decibels = 10 x log (I1/I2)

I1 = 20, I2 = 10: # decibels = 10 x log 2 = 3I1 = 100, I2 = 10: # decibels = 10 x log 10 = 10I1 = 400, I2 = 4: # decibels = 10 x log 100 = 20


Sound intensity

Strictly speaking decibel is a relative unit only

For humans, it only makes sense as “relative to the softest sound a human ear can hear”

0 db is baseline (not silence, or no sound …)

Often threshold of hearing at 1000Hz

Threshold of pain is 120 db (1012 x louder than 0 db !!)


Sound waves


Sound waves

Lecture 3: Images Intro to IT

Overview 01010100001010101010100110100010101001101001010010100011100010101010100101111001001010…


Digitising Sound

Sampling: how often discrete readings are taken (from a continuous signal)Rate (Hz) Quality11,025 AM Radio22,050 FM Radio44,100 CD48,000 DAT96,000-192,000 DVD


How often to sample?

Nyquist (or Nyquist-Shannon): Need to sample at least two points in each cycle to perfectly reconstruct the sound wave

Humans can hear approximately 20 to 20,000 Hz

Most sensitive in range 2,000 Hz to 5,000 Hz

11,025 Hz often works for speech (up to 5,000 Hz) but not music


Quantisation

Once we have a sample, how many different values do we allow for it?

More values means better quality, but larger file size

BITDEPTH


Quantisation

Same issues as for images:

More sampling, more quantised levels better quality larger file size

Dynamic range: range of possible quantised values will `clip’ some sounds if too narrow will waste accuracy if too wide


Conclusion Go to laboratory classes (and tutorials) this

week!

Work on Assignment 1

Keep reading! (book particularly)

Documents

COSC1078 Introduction to Information Technology Lecture 5 Audio