Lecture 6: Audio Intro to IT

COSC1078 Introduction to Information Technology

Lecture 6

AudioJames Harland

james.harland@rmit.edu.au

Lecture6: 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 6: Audio Intro to IT

Overview

Questions?

Assignment 1

Audio

Questions?

Lecture 6: Audio 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 6: Audio SE Fundamentals

Questions?

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

This week?

Lecture 6: 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 6: 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 6: 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 6: Audio Intro to IT

Overview

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Lecture 6: Audio Intro to IT

Digitising Sound

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

Quantisation: howmany different values each element can have

Lecture 6: Audio Intro to IT

Audio vs Images

One of the biggest differences between images and audio is ….

TIME

Lecture 6: Audio Intro to IT

Audio and Time

Adds a dimension to file size (sampling, quantisation, channels, time, …)

Streaming rate can be too slow Playback needs to be continuous Time to listen to audio is fixed

How long does it take to view an image? How long does it take to listen to an entire CD?

Lecture 6: Audio Intro to IT

Audio file sizes

How much space is needed for 1 minute on a CD?

Two channels (stereo) 16 bits per channel (bit depth) (65,536 quanta)

Sampling rate of 44,100 Hz

60 s x 44,100 samples/s x 16 bits/sample x 2 = 84,672,000 bits = 10,584,000 bytes≈ 10 MBSo an 800MB CD can hold about 80 minutes of music….

Lecture 6: Audio Intro to IT

Audio file sizes

How much space is needed for 90 minutes on a DVD?

Surround sound is 5.1 channels 16 bits per channel (bit depth) (65,536 quanta)

Sampling rate of 192,000 Hz

90 min x 60 s x 192,000 samples/s x 16 bits/sample x 5.1 = 84,602,880,000 bits = 10,575,360,000 bytes≈ 9.8 GB

Lecture 6: Audio Intro to IT

Audio file sizes

How much space is needed for 90 minutes of a human voice on a DVD?

Mono (ie one channel) would be fine 8 bits per channel (bit depth) (256 quanta) Sampling rate of 11,025 Hz

90 min x 60 s x 11,025 samples/s x 8 bits/sample = 476,280,000 bits = 59,535,000 bytes≈ 56 MBSo adding 3 extra ‘voice over’ tracks only adds about 168 MB to an 8 GB DVD …

Lecture 6: Audio Intro to IT

Audio file sizes

To reduce file size:

Reduce sampling rate Reduce bit depth 8 bits will work for speech, but not music

Reduce channels (ie just mono) Halves file size – could work for games

(Reduce duration? Unlikely ) Use compression techniques Be aware of lossy vs lossless compression

Lecture 6: Audio Intro to IT

MP3

MPEG-1 Audio Layer 3

Lossy compression (ie loses some information) (so don’t use this for `master’ copies when editing) Reduces size by factor of 11 compared to CD Reduces accuracy of sounds which are unlikely tobe heard Based on `psychoacoustic models’ Emerged in early 1990’s

(Moving Picture Experts Group)

Lecture 6: Audio Intro to IT

MIDI

Musical Instrument Digital Interface

Purely digital music created by a processor Often used as a keyboard attached to a computer Note information from a digital source Small size (60s in 2KB) Easily edited Sound depends on localdevice

Lecture 6: Audio Intro to IT

Conclusion

Go to laboratory classes (and tutorials) this week!

Do online quizzes later this week

Keep reading! (book particularly)