Digital Media

1. Digital Media Lecture 2.1: SemesterOverview Georgia Gwinnett College School of Science and Technology Dr. Jim Rowan

2. Refer to Supplemental text: • Counting like an alien • Networking issues • Sound and Sampling

3. The Big Question: • How do you take stuff found in the real world… • Store it as numbers on a computer… • So that it can be manipulated and shared?

4. The answer: • It depends on what it is you are trying to capture • We will have to know about the nature of the real world • Some things can be counted • Some things need to be measured • The details of this will come a bit later

5. As previously seen using hexFiend: • Text, audio, images and videos are all stored in a file as numbers on the computer • Some of this is meant for human consumption (ASCII) • Some of this is meant for program consumption (the header) • Some is used by the program to save and represent the world • http://wiki.ggc.edu/wiki/It%27sAllJustBitsITEC2110WikiTextJrowan1 • Let’s get started: It’s all just bits!

6. But first: Numbering systems! • Which is correct? 5 + 5 = 10 1 + 1 = 10 1 + 7 = 10 1 + F = 10

7. But first: Numbering systems! • Which is correct? • The answer is: It depends! 5 + 5 = 10 (in decimal) 1 + 1 = 10 (in binary) 1 + 7 = 10 (in octal) 1 + F = 10 (in hexadecimal)

8. But first: Numbering systems! • In this class we deal with • Decimal • Binary • Hexadecimal • We will not be converting • We will not do math (a small lie) • We will learn how to count • http://wiki.ggc.edu/wiki/HowToCountLikeAnAlien • Let’s get started: Counting like an alien!

9. The process of counting is simple • No matter which numbering system… • You count starting with the first digit • You continue to count through all the digits available to you • When you run out of digits, you go back to the first digit • Add 1 to the column to the left

10. How many things can you count if you have 4 [your numbering system here]positions? • In decimal: 0000 -> 9999 • You can count 10,000 things • In binary: 0000 -> 1111 • You can count 16 things • In hexadecimal: 0000 -> FFFF • You can count 65,536 things

11. How many things can you count if you have 4 [your numbering system here]positions? • The formula is: • the number of digits in the numbering system raised to the power of the number of positions you are using • [#digits in the system] ** [# positions used together] • In decimal: 0000 -> 9999 10 ** 4 = 10,000 things • In binary: 0000 -> 1111 2 ** 4 = 16 things • In hexadecimal: 0000 -> FFFF 16 ** 4 = 65,536 things

12. How do you convert stuff in the real world into numbers that can be placed on a computer? • It depends… • It depends on whether the thing is a discrete thing or a continuous thing

13. Stuff (phenomena) in the real world… • Can be discrete • These either ARE or ARE NOT • These can be counted • The number of cars in a parking lot • The number of beans in a jar • Can be continuous • These have no breaks • These must be measured • The height of a wave • The atmospheric pressure

14. Stuff (phenomena) in the real world… • Discrete can be counted • 5 cars • 11,223 beans • Continuous must be MEASURED • The height of a wave • 3.76 feet from crest to trough • The atmospheric pressure • 30.02 inches of mercury

15. The problem is… • Most of the interesting stuff is continuous! • Sound is continuous compression waves • Light is continuous electromagnetic waves • To store continuous phenomena on a computer you must measure it and store the measurement

16. Sampling: • The process of converting continuous phenomena into discrete so that you can store it as a number on the computer

17. But before we talk about sampling…What this stuff means: • Bit: binary digit • Byte: 8 Bits • KB: kilo byte (1,000 bytes) • MB: mega byte (1,000,000 bytes) • GB: giga byte (1,000,000,000 bytes) • TB: tera byte (1,000,000,000,000 bytes) • KBPS: kilo (1,000) bits per second • MBPS: mega (1,000,000) bits per second

18. What this stuff means:Strictly speaking… • In computing the meanings of K, M, G are powers of 2 K = 2 ** 10 = 1,024 not 1,000 M = 2 ** 20 = 1,048,576 not 1,000,000 G = 2 ** 30 = 1,073,710,825 not 1,000,000,000 • But in this class, either will do

19. What this stuff means:And finally… • In some classes B and b when used in abbreviations mean Bytes and bits respectively • This can be confusing • For this class… • When abbreviating communication speeds the b (or B) means bits • When abbreviating file size the b (or B) means bytes

20. What this stuff means:So… • Since kbps (or KBPS) is a communication speed the b (or B) means bits • Since mb (or MB) is a file size the b (or B) means bytes

21. Network access • Changing all the time • Is getting faster and faster • Is available in a variety of forms • In this class we will discuss a few of them http://wiki.ggc.edu/wiki/NetworkingIssues Let’s get started: Networking issues

22. Network access • Can be symmetric • The speed into the network is the same as the speed out • But now asymmetric is fairly common in the home • The speed out of the network is faster than the speed into the network • Unless you are running a server • Servers usually have very high speed, symmetric connections to the network

23. Network access • ADSL example • Asymmetric Digital Subscriber Line • Speed in can be 640 kbps • Speed out can be 6.1 mbps • Prehistoric example: dial up modem • Asymmetric • Speed in is 36,000 bps • Speed out as high as 56,000 bps

24. Network access • If you are running a commercial server (like you would have if you were running an online business) you may want faster service • T1 and T3 are faster and symmetric • T1 can be 1.544 mbps • T3 can be 44.7 mbps

25. And now… Sampling • How many samples do you need to faithfully capture a continuous phenomena? • The answer: • It depends! (of course!) • What does it depend on? • It depends on the frequency of the continuous phenomena you are trying to capture http://wiki.ggc.edu/wiki/SoundInTheRealWorldAndSampling Capturing sound in the real world? Sampling!: Sound and Sampling

26. Sampling sound • Sound radiates out from the source like the waves created when you toss a stone into a pond • In the air it travels at ~760 mph

27. How many samples are needed? • Now, an example to show how and why the Nyquist rate works • Below is a note played on a violin and captured with an oscilloscope

28. A note played on a violin Sampled at 625 samples per second

29. A note played on a violin Sampled at 1250 samples per second

30. A note played on a violin Sampled at 2500 samples per second

31. A note played on a violin Sampled at 5000 samples per second

32. A note played on a violin Sampled at 10,000 samples per second

33. A note played on a violin Sampled at 20,000 samples per second

34. How many samples are needed? • If you take too few samples • the sound quality will degrade • but the file size will be small • If you take too many samples • the sound quality will be excellent • but the file size can get HUGE! • So… • Where’s the sweet spot?

35. How many samples are needed? • Nyquist states that you need to sample at twice the frequency of the highest frequency you want to capture and faithfully reproduce • With humans • Since some of us can hear 20,000 cps • You would need to sample at 40,000 cps • CD quality? (with a little wiggle room) • 44,100 samples per second

36. An example: Fields of Gold • We played Fields of Gold in class • CD quality is: • 44,100 samples per second • 16 bits (2 bytes) per sample • with 16 bits you can capture… • 2**16 = 65,536 different levels • Looking at the file: • It is 4 minutes and 59 seconds • The file size is 1,201,173 bytes long • Does this make sense?

37. An example: Fields of Gold 4 minutes and 59 seconds = 4 x 60 + 59 = 299 seconds 299 seconds x 44,100 sps = 13,156,000 samples 13,156,000 samples x 2 bytes per sample = 26,371,800 bytes But this is stereo (two channels) so… 26,371,800 bytes x 2 channels… = 52,743,600 bytes… That’s ~52 MB… but we said that the music was 1.2 MB How is this possible? HMMMMMmmmm…

38. An example: Fields of Gold Fields of Gold is an MP3… It’s compressed! If we had the original CD it would be ~52 MB in length

39. Types of compressed files • MP3 is lossy • What you get back after compressing the file is NOT exactly the same as the original • But… it’s close enough • Images and sound can use lossy compression techniques (more later) • Zip is lossless • What you get back is EXACTLY what you started with • Applications must be losslessly compressed • All the 0s and 1s have to be exactly the same or the program will not run

40. Sampling • The process used to convert continuous phenomena in the real world to discrete numbers stored on a computer • But… this process makes an “alias” of the original; it’s an approximation of the original that does have faults • These negative side effedts are called artifacts

41. Sampling artifact examples: • With audio, one artifact is quantization hiss • With video, one artifact is retrograde motion; wheels look to turn backwards • http://wiki.ggc.edu/images/3/35/RetrogradeGMCarcadiaBroadbandHigh.mov • http://wiki.ggc.edu/images/8/85/JrowanSpring2012CroppedRetrogradeMotionClip.mov • Moving images: Film • With images one artifact is posterization • http://wiki.ggc.edu/wiki/BitmappedImageDitheringPosterizationjrowanSummer2012 • Images as piles of numbers: Bitmapped images: Dithering and posterization

42. A brief look at the Internet • http://wiki.ggc.edu/wiki/NetworkingIssues • Let’s get started: Networking issues

43. A brief look at the Internet:How to request stuff • Uniform Resource Locator (URL) • http://www.amazon.com/newStuff/index.html • Has 3 parts • Protocol • HTTP:// • FTP:// • SMTP:// • Domain name • Ends in .edu .com .gov .org • Directory structure and the requested page • /newStuff/index.html • http://wiki.ggc.edu/wiki/NetworkingIssues • Let’s get started: Networking issues

44. A brief look at the Internet:How to request stuff • Uniform Resource Locator (URL) • http://www.amazon.com/newStuff/index.html • Has 3 parts • Protocol • HTTP:// • FTP:// • SMTP:// • Domain name • Ends in .edu .com .gov .org • Directory structure and the requested page • /newStuff/index.html • http://wiki.ggc.edu/wiki/NetworkingIssues • Let’s get started: Networking issues

45. A brief look at the Internet:How to request stuff • Uniform Resource Locator (URL) • http://www.amazon.com/newStuff/index.html • Has 3 parts • Protocol • HTTP:// • FTP:// • SMTP:// • Domain name • Ends in .edu .com .gov .org • Directory structure and the requested page • /newStuff/index.html • http://wiki.ggc.edu/wiki/NetworkingIssues • Let’s get started: Networking issues

46. A brief look at the Internet • http://wiki.ggc.edu/wiki/NetworkingIssues • Let’s get started: Networking issues

47. A brief look at the Internet • http://wiki.ggc.edu/wiki/NetworkingIssues • Let’s get started: Networking issues