Lecture 6: Audio Intro to IT COSC1078 Introduction to Information Technology Lecture 6 Audio James Harland

Lecture 6: AudioIntro 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 ITAssignment 3, Peer and Self Assessment

Lecture 6: AudioIntro to IT Overview  Questions?  Audio  Assignment 1  Questions?

Lecture 5: AudioIntro to IT Introduction James Harland URL: Phone: Office: (Building 14, level 8, room 13) Consultation: Wed , Thu Where is my office?

Lecture 6: AudioIntro to IT Overview …

Lecture 6: AudioIntro to IT Digitising Sound Sampling: how often discrete readings are taken (from a continuous signal) Quantisation: how many different values each element can have

Lecture 6: AudioIntro to IT Audio vs Images One of the biggest differences between images and audio is …. TIME

Lecture 6: AudioIntro 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: AudioIntro 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 MB So an 800MB CD can hold about 80 minutes of music….

Lecture 6: AudioIntro 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: AudioIntro 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 to be heard  Based on `psychoacoustic models’  Emerged in early 1990’s (Moving Picture Experts Group)

Lecture 6: AudioIntro 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 local device

Lecture 5: AudioIntro 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: AudioIntro to IT Assignment 1

Lecture 5: AudioIntro 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)