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 to IT

1 Introduction

2 Images

3 Audio

4 Video WebLearn Test 1

5 Computer Fundamentals Assignment 1

6 Computer Fundamentals

7 Computer Fundamentals

8 Operating Systems WebLearn Test 1

9 Operating Systems Assignment 2

10 Internet

11 Internet Security   WebLearn Test 3

12 Future of IT Assignment 3, Peer and Self Assessment

Lecture 5: Audio Intro to IT

Overview

Questions?

Audio

Assignment 1

Questions?

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: 14.8.13 (Building 14, level 8, room

13)• Consultation: Wed 1.30-2.30, Thu 11.30-12.30

Where is my office?

Lecture 3: Images 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

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

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

Assignment 1

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

Address two issues in relation to this

Lab classes 2 and 3 based around GIMP

Main emphasis is on process, not result!

Is in the Learning Hub

Lecture 5: Audio Intro to IT

Assignment 1

Lecture 5: Audio Intro to IT

Conclusion

Go to laboratory classes (and tutorials) this week!

Web Test next week (week 4)

Do online quizzes later this week

Keep reading! (book particularly)