Lecture 5: Audio Intro to IT

COSC1078 Introduction to Information Technology

Lecture 5

AudioJames Harland

james.harland@rmit.edu.au

Lecture 5: Audio Intro to IT

Introduction

James Harland• Email: james.harland@rmit.edu.au• 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-

12.30

What is the view like from my office?

Lecture 5: Audio Intro to IT

Overview

Questions?

Assignment 1

Audio

Questions?

Lecture 4: Images Intro to IT

Introduction to IT

1 Introduction

2 Images

3 Audio

4 Video WebLearnTest 1

5 Binary Representation Assignment 1

6 Data Storage

7 Machine Processing

8 Operating Systems WebLearn Test 1

9 Processes Assignment 2

10 Internet

11 Internet Security   WebLearn Test 3

12 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?

Lecture 5: Audio Intro to IT

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%

Lecture 5: Audio Intro to IT

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)

Lecture 5: Audio Intro to IT

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

Lecture 5: Audio Intro to IT

Assignment 1

Lecture 5: Audio Intro to IT

Overview

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Lecture 5: Audio Intro to IT

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’’ )

Lecture 5: Audio Intro to IT

Frequency

How many complete cycles within a unit of time

Higher frequency means higher pitch

Lecture 5: Audio Intro to IT

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

Lecture 5: Audio Intro to IT

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 !!)

Lecture 5: Audio Intro to IT

Sound waves

Lecture 5: Audio Intro to IT

Sound waves

Lecture 3: Images Intro to IT

Overview

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Lecture 5: Audio Intro to IT

Digitising Sound

Sampling: how often discrete readings are taken (from a continuous signal)Rate (Hz) Quality

11,025 AM Radio

22,050 FM Radio

44,100 CD

48,000 DAT

96,000-192,000 DVD

Lecture 5: Audio Intro to IT

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

Lecture 5: Audio Intro to IT

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

Lecture 5: Audio Intro to IT

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

Lecture 5: Audio Intro to IT

Conclusion

Go to laboratory classes (and tutorials) this week!

Work on Assignment 1

Keep reading! (book particularly)