1. Digital Media Dr. Jim Rowan Chapter 2

2. Roll Call using Banner

3. Project 1 preliminary Details to be posted on the class projects page Podcast using Audacity Import music Do a voice-over Post the result on your wiki site

4. The Question: How do you put stuff in a computer –so that you can manipulate it –so that you can send it –so that someone else can see and use it? How do you represent the real world in a digital world?

5. The answer: Represent the real world as numbers Store the numbers Retrieve the numbers Display them in a form humans understand

6. Today: Chapter 2 is a “first cut” of nearly all the material that will be covered in greater detail this semester About the real world About digital representationa

7. File formats and extensions Indication to us (the humans) what kind of file this is Some software looks at the extension –so... some software will try to open files with improper extensions –results in “file corrupted” error message –try it... change the extension from.doc to.jpg

8. File formats and extensions Some software looks at the data in the file for more definitive answer –important file-related information is encoded in the data of the file for example: some image formats have color tables to reduce the size of the file some video just saves the changes from one frame to the next

9. Numbering systems Humans: decimal –Humans: 10 fingers, 10 digits: –0, 1, 2, 3, 4, 5, 6, 7, 8 & 9 Computers: binary –Computers: 2 fingers, 2 digits –0 & 1

10. Binary Coding Data for a computer –zeros and ones, –off and on –false and true Data for humans –Coding schemes are used by humans to reduce the volume of digits –Two coding schemes used Hexadecimal ASCII

11. Hexadecimal Humans and Computers: hexadecimal –Hexadecimal: 16 fingers, 16 digits –Humans organize 0s and 1s into groups of 4 –These groups of 4 are can be represented by a single hexadecimal digit –0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F

12. ASCII Humans and Computers: ASCII –Made of two hexadecimal codes –One ASCII character - two hex codes –ASCII code for R (from text pg 317) hexadecimal: 52 binary: 0101 0010

13. How to count using a different number of fingers 10 fingers: Counting in decimal –0, 1, 2, 3, 4, 5, 6, 7, 8, 9, –start over but put a 1 in the higher position 2 fingers: Counting in binary –0, 1 –start over but put a 1 in the higher position 16 fingers: Counting in hexadecimal –0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F –start over but put a 1 in the 1 higher position

14. From the Real World to Stuff on a computer A note –Paper and pen -> bits (0s and 1s) A picture –Reflected light -> bits (0s and 1s) A song –Pressure waves in air -> bits (0s and 1s) A video –Pressure waves in air and Reflected light -> bits (0s and 1s)

15. Phenomena in the Real world: discrete vs continuous Things in the real world can be discrete They either ARE or ARE NOT there These things can be counted Examples: –The number of cars in the parking lot –The number of beans in a jar

16. Phenomena in the Real world: discrete vs continuous Things in the real world can be continuous Continuous can’t be counted, it must be measured Examples: –Atmospheric pressure –Height of an ocean wave –Frequency of a sound wave

17. But... computers can only count Discrete data is easy for a computer –count it and store it as a number Continuous data... not so much –music: measure the frequency & amplitude encode as discrete –pictures: measure the amount of light and its color encode as discrete

18. [Switch to Mac] Play/show some stuff Text (using Text Edit) Audio (using Quicktime) Image (using Preview) Video (using Quicktime) Open same stuff (using HexFiend) Text Audio Image Video (open and crop jayley and manOfScience)

19. Note on paper

20. Picture

21. Song: fieldsOfGold.mp3

22. Video

23. Question... Computers only store 0s and 1s –They only store digits... So... How does all this continuous stuff end up in a computer so that we can save it and play it back? Continuous data must be converted to discrete data

24. Converting Continuous (analog) data to Discrete data Requires two processes –sampling - equally spaced –quantization - measuring at each sample Usually handled by –analog to digital converter –AKA A to D converter or ADC

25. Digital back to the real world: –Display samples using “sample and hold” –Play the sample for the duration of the sample time Converting Discrete data back to Continuous (analog) data

26. But... How many samples?

29. single sample

31. two samples

33. three samples

35. four samples

37. five samples

39. How frequently should I sample? too few –small file size (good) –not a faithful representation when replayed too many –large file size (bad) –excellent representation when replayed The Nyquist rate –twice as many samples as the frequency –ok file size –faithful representation when replayed

40. Nyquist rate Why is the sample size used for audio CDs 44,000 samples per second? –Human hearing response is in the range of 0 to 22,000 cycles per second Why is the sample size used for audio CDs 44,000 samples per second? –Human hearing response is in the range of 0 to 22,000 cycles per second

41. FieldsOfGold.mp3 4 minutes and 59 seconds long 1,201,173 bytes in length Does this make sense? 4 minutes and 59 seconds long –299 seconds 44,000 samples per second (sample rate) 16 bit samples (quantity stored for each sample)

42. FieldsOfGold.mp3 4’59 = 299 seconds long 299 x 44,000 samples per second = 13,156,000 bytes 13,156,000 x 2 bytes/sample –26,312,000 bytes Should be 26.3 megabytes! Why only 1.2 megabytes? HMMMmmm...

43. FieldsOfGold.mp3 Why 26.3 megabytes not 1.2 megabytes? This is an MP3! Data COMPRESSION!

44. Undersampling & Video Retrograde Motion

45. Further reading http://en.wikipedia.org/wiki/Nyquist_rate http://en.wikipedia.org/wiki/Sampling_% 28signal_processing%29 http://en.wikipedia.org/wiki/Mp3

46. Sampling Artifacts Under-sampling (too few samples) of continuous data can produce undesired artifacts –audio distortion –jagged edges on images –Moire’ patterns on images –retrograde motion on video

47. Sampling Artifacts (cont.) Not enough quantization levels when sampling continuous data can produce undesired artifacts Images –too few color: colors look artificial –loss of fine distinction –too few grey levels: gradients become steps –too few brightness levels: posterization

48. Sampling Artifacts (cont.) Not enough quantization levels when sampling continuous data can produce undesired artifacts Audio –too few amplitude levels, quantization noise - hiss 8 bits (256 amplitude levels) produces discernable noise 16 bits (65536 amplitude levels) CD quality, no discernable hiss –general sound “fuzziness”

49. Multimedia Hardware Requirements Multimedia consumption? –requires only a lower powered machine Multimedia production? –requires a more powerful computer –consider “fields of gold.mp3” 26+megabytes of data uncompressed 1.2 megabytes of data compressed –images are produced in layers then flattened for consumption

50. Hardware requirements Video capture requires large areas of contiguous disk space Frequent disk defragmentation is required http://en.wikipedia.org/wiki/Defragmentatio n

51. defragmentation black is occupied space white is available space memory before memory after largest contiguous space is 5 largest contiguous space is 11 and there are 6 of these

52. Hardware requirements: Form factor... screen real estate makes a difference –size is smaller? –can/should affect the format of the display cannot simply display the same page on –a desktop computer –a cell phone –a pda

53. Hardware requirements Form factor... Displayed unmodified laptop display of my GGCwiki site Treo LG VX3400

54. Hardware... RAID Redundant Array of Inexpensive Disks Designed as a hardware failsafe –multiple copies of the same data Can be used to speed data transfer –(you may need this in multimedia production) http://en.wikipedia.org/wiki/RAID

55. RAID redundant 94731990 disk #1 disk #2 disk #3 disk #4 disk #5 disk #6 disk #7 disk #8

56. RAID overlapped (fast) 7 3 1 9 9 4 0 9 94731990 disk #1 disk #2 disk #3 disk #4 disk #5 disk #6 disk #7 disk #8

57. Networks Local Area Network (LAN) –local routers, bridges, switches... Internet –Uses TCP/IP protocol (the rules your communication must follow) –http://en.wikipedia.org/wiki/TCP/IP –you get access through an ISP

58. Network access... dial up connection –phone modem –limited to 56,000 bps (bits, not bytes) max downstream (internet to modem) –33.6 kbps upstream (modem to internet) –rarely get these speeds

59. Network access... ADSL –asymmetric digital subscriber line –over copper phone wires –limited to short distance from phone switch –6.1 mbps (million bps) downstream –640 kbps upstream

60. Network access... Other options –Cable modem (also asynchronous) –satellite with phone (also asynchronous) –satellite alone (expensive but available in the boonies) –local wireless networks –high altitude tethered balloons –transmission over power lines

61. Commercial internet users Provide web servers for others to put websites on Large commercial enterprises will have their own web server T1 connection 1.544 mbps T3 connection 44.7 mbps

62. Servers & Clients... Clients consume internet content Your browser is a client Clients request content from servers –by sending a server an HTTP://URL message which is a request for a web page Servers respond to requests for internet content –send requested web pages to Clients The content is sent in HTML code –HTML is interpreted by the client (browser) and displayed on your machine

63. Servers & Clients... URL is a human-readable name uniform resource locator takes the form www.amazon.com/newStuff/index.html The domain name: www.amazon.com The file you want to see is: newStuff.index.html the name maps to a number called an IP address http://en.wikipedia.org/wiki/IP_address

64. Servers & Clients... servers have fixed IPs so they are easy to find your computer probably uses DHCP which is a dynamic (changing) IP An example: my IP right now (assigned through dhcp) is: 10.0.106.91 my IPv6 address (new addressing scheme) is fe80:0000:0000:0000:0211:24ff:fe8f:abb6

65. yahoo.com (server) 235.01.30.564 The Internet you at home running a browser (client) DHCP: walmart.com (server) 100.43.153.07 ggc.usg.edu (server) 145.67.33.73

66. yahoo.com (server) 235.01.30.564 The Internet you at home running a browser (client) DHCP: 10.0.91.35 walmart.com (server) 100.43.153.07 ggc.usg.edu (server) 145.67.33.73 ISP

67. yahoo.com (server) 235.01.30.564 The Internet www.yahoo.com = 235.01.30.564 you at home running a browser (client) http://www.yahoo.com walmart.com (server) 100.43.153.07 ggc.usg.edu (server) 145.67.33.73

68. yahoo.com (server) 235.01.30.564 The Internet you at GGC running a browser (client) DHCP: walmart.com (server) 100.43.153.07 ggc.usg.edu (server) 145.67.33.73

69. yahoo.com (server) 235.01.30.564 The Internet you at GGC running a browser (client) DHCP: 322.21.5.36 walmart.com (server) 100.43.153.07 ggc.usg.edu (server) 145.67.33.73 ISP

70. yahoo.com (server) 235.01.30.564 The Internet www.walmart.com = 100.43.153.07 you at starbucks running a browser (client) HTTP://www.walmart.com walmart.com (server) 100.43.153.07 ggc.usg.edu (server) 145.67.33.73

71. MIME types Multipurpose Internet Mail Extension Allows the transmission of more than just ASCII text (like you’d expect in an email) MIME types are specified in the header Huge variety of MIME types are allowed –audio, images, video –compressed files

72. A word about standards Standards allow cooperation But standards require agreement Works well during slow growth But in a rapidly changing environment... –frequently obsolete before adopted One company may dominate the market becoming the de-facto standard

73. Questions?