1. Lecture 5: Audio Intro to IT COSC1078 Introduction to Information Technology Lecture 5 Audio James Harland james.harland@rmit.edu.au

2. Lecture 5: AudioIntro to IT Introduction to IT 1 Introduction 2 Images 3 Audio 4 Video 5 Binary Representation WebTest 1, 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 ITAssignment 3, Peer and Self Assessment

3. Lecture 5: AudioIntro to IT Overview  Questions?  Audio  Assignment 1  Questions?

4. Lecture 3: ImagesIntro 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 2.00-3.00, Thu 12.30-1.30 What is the view like from my office?

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6. Lecture 5: AudioIntro 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’’ )

7. Lecture 5: AudioIntro to IT Frequency  How many complete cycles within a unit of time  Higher frequency means higher pitch

8. Lecture 5: AudioIntro 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 (I 1 /I 2 ) I 1 = 20, I 2 = 10: # decibels = 10 x log 2 = 3 I 1 = 100, I 2 = 10: # decibels = 10 x log 10 = 10 I 1 = 400, I 2 = 4: # decibels = 10 x log 100 = 20

9. Lecture 5: AudioIntro 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 (10 12 x louder than 0 db !!)

10. Lecture 5: AudioIntro to IT Sound waves

11. Lecture 5: AudioIntro to IT Sound waves

12. Lecture 3: ImagesIntro to IT Overview 01010100001010101010100110100010101001101001010010 100011100010101010100101111001001010…

13. Lecture 5: AudioIntro to IT Digitising Sound Sampling: how often discrete readings are taken (from a continuous signal) Rate (Hz)Quality 11,025AM Radio 22,050FM Radio 44,100CD 48,000DAT 96,000-192,000DVD

14. Lecture 5: AudioIntro 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

15. Lecture 5: AudioIntro 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 BIT DEPTH

16. Lecture 5: AudioIntro 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

17. Lecture 5: ImagesIntro 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  Address three issues in relation to this  Lab classes 2 and 3 will be based around GIMP  Lab class 4 based on Audacity  Main emphasis is on process, not result!  In the Blackboard later today

18. Lecture 5: AudioIntro to IT Assignment 1

19. Lecture 5: AudioIntro to IT Conclusion  Go to laboratory classes (and tutorials) this week!  Work on Assignment 1  Keep reading! (book particularly)