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									   Data Storage – Part 2

CS 1 Introduction to Computers and Computer
                 Technology
                Rick Graziani
                   Fall 2010
Digitizing Text




• Earliest uses of PandA (Presence and Absence) was to digitize text
    (keyboard characters).
•   We will look at digitizing images and video later.
•   Assigning Symbols in United States:
     – 26 upper case letters
     – 26 lower case letters
     – 10 numerals
     – 20 punctuation characters
     – 10 typical arithmetic characters
     – 3 non-printable characters (enter, tab, backspace)
     – 95 symbols needed
Rick Graziani graziani@cabrillo.edu                                    2
ASCII-7
• In the early days, a 7 bit
  code was used, with 128
  combinations of 0’s and 1’s,
  enough for a typical
  keyboard.
• The standard was developed
  by ASCII (American
  Standard Code for
  Information Interchange)
• Each group of 7 bits was
  mapped to a single keyboard
  character.
     0 = 0000000
     1 = 0000001
     2 = 0000010
     3 = 0000011
… 127 = 1111111
Rick Graziani graziani@cabrillo.edu   3
Byte

Byte = A collection of bits (usually 7 or 8 bits) which
  represents a character, a number, or other information.
• More common: 8 bits = 1 byte
• Abbreviation: B




Rick Graziani graziani@cabrillo.edu                         4
Bytes

1 byte (B)

Kilobyte (KB) = 1,024 bytes (210)
• “one thousand bytes”
   1,024 = 2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 * 2 * 2

Megabyte (MB) = 1,048,576 bytes (220)
• “one million bytes”

Gigabyte (GB) = 1,073,741,824 bytes (230)
• “one billion bytes”

Rick Graziani graziani@cabrillo.edu                5
    ASCII-8

• IBM later extended the
                                          1
    standard, using 8 bits per
    byte.
•   This was known as
    Extended ASCII or ASCII-8
•   This gave 256 unique
    combinations of 0’s and 1’s.

    0 = 00000000
    1 = 00000001
    2 = 00000010
    3 = 00000011
… 255 = 11111111



    Rick Graziani graziani@cabrillo.edu       6
ASCII-8




Rick Graziani graziani@cabrillo.edu   7
Try it!                                           1




• Write out Cabrillo College (Upper and Lower case) in bits (binary)
    using the chart above.

0100 0010               0110 0001     …
     C                       a


Rick Graziani graziani@cabrillo.edu                                    8
The answer!                                                      1




0100 0011            0110 0001         0110 0010   0111 0010   0110 1001   0110 1100
   C                     a                b           r            i           l
0110 1100            0110 1111        0010 0000    0100 0011   0110 1111   0110 1100
     l                   o               space        C           o             l
0110 1100            0110 0101        0110 0111    0110 0101
     l                   e                 g            e

Rick Graziani graziani@cabrillo.edu                                                    9
ASCII ART




•   http://patorjk.com/software/taag/
Rick Graziani graziani@cabrillo.edu     10
Rick Graziani graziani@cabrillo.edu   11
Unicode




• Although ASCII works fine for English, many other languages need
    more than 256 characters, including numbers and punctuation.
•   Unicode uses a 16 bit representation, with 65,536 possible symbols.
•   Unicode can handle all languages.
•   www.unicode.org
Rick Graziani graziani@cabrillo.edu                                       12
        Non-text Files:
Representing Images and Sound
Rick Graziani graziani@cabrillo.edu   14
Rick Graziani graziani@cabrillo.edu   15
Pixels




•   A monitors screen is divided into a grid of small unit called
    picture elements or pixels.
•   The more pixels per inch the better the resolution, the
    sharper the image.
•   All colors on the screen are a combination of red, green
    and blue (RGB), just at various intensities.


Rick Graziani graziani@cabrillo.edu                                 16
Rick Graziani graziani@cabrillo.edu   17
• Each Color intensity of red, green and blue represented as a
    quantity from 0 through 255.
•   Higher the number the more intense the color.
•   Black has no intensity or no color and has the value (0, 0, 0)
•   White is full intensity and has the value (255, 255, 255)
•   Between these extremes is a whole range of colors and intensities.
•   Grey is somewhere in between (127, 127, 127)
Rick Graziani graziani@cabrillo.edu                                      18
RGB Colors and Binary Representation

• You can use your favorite program that allows you to choose colors to
    view these various red, green and blue values.




 Rick Graziani graziani@cabrillo.edu                                      19
RGB Colors and Binary Representation




• Let’s convert these colors from Decimal to Binary!
                                      Red   Green   Blue
      Purple:                         172    73     185
      Gold:                           253   249      88




Rick Graziani graziani@cabrillo.edu                        20
RGB Colors and Binary Representation

                                      Red   Green    Blue
   Purple:                            172    73      185
   Gold:                              253   249       88
Number of:
         27   26  25                          24      23 22     21 20
     128’s 64’s 32’s                        16’s    8’s 4’s   2’s 1’s
Dec.
172
73
185

253
249
88
Rick Graziani graziani@cabrillo.edu                                     21
RGB Colors and Binary Representation

                                      Red       Green    Blue
   Purple:                            172        73      185
   Gold:                              253       249       88
Number of:
         27   26  25                              24      23 22       21 20
     128’s 64’s 32’s                            16’s    8’s 4’s     2’s 1’s
Dec.
172      1    0    1                              0      1      1    0    0
73       0    1    0                              0      1      0    0    1
185      1    0    1                              1      1      0    0    1

253                1                  1     1     1      1      1    0    1
249                1                  1     1     1      1      0    0    1
88                 0                  1     0     1      1      0    0    0
Rick Graziani graziani@cabrillo.edu                                           22
RGB Colors and Binary Representation




• We have now converted these colors from Decimal to Binary!
                                      Red    Green     Blue
      Purple:                         172     73       185
                              10101100      01001001   10111001


      Gold:                           253    249        88
                              11111101      11111001   01011000


•   Why does this matter?
Rick Graziani graziani@cabrillo.edu                               23
First a word about Pixels Per Inch
                                                     1600 pixels
   1200 pixels/300 ppi = 4 inches              1600 pixels /300 ppi = 5.3 inches
                                      1200
                                      pixels


graphicssoft.about.com
• PPI stands for pixels per inch.
• PPI is a measurement of image resolution that defines the
  size an image will print.
• The higher the PPI value, the better quality print you will
  get--but only up to a point.
• 300ppi is generally considered the point of diminishing
  returns when it comes to ink jet printing of digital photos.
Rick Graziani graziani@cabrillo.edu                                                24
First a word about Pixels Per Inch

•   The higher the PPI value,
    the better quality print you
    will get--but only up to a
    point.




Rick Graziani graziani@cabrillo.edu   25
 RGB Colors and Binary Representation




                                        Red      Green     Blue
     Purple:                            172       73       185
                             10101100          01001001    10111001


                                         24 bits for one pixel!

• “True color” systems require 3 bytes or 24 bits per pixel.
• There is 8 bit and 16 bit color, which gives you less of a color palette.



  Rick Graziani graziani@cabrillo.edu                                         26
 RGB Colors and Binary Representation


          8 inches or                           10 inches or
          2,400 pixels                          3,000 pixels


                                       Red    Green     Blue
    Purple:                            172     73       185
                            10101100         01001001   10101111   = 24 bits per pixel
• An 8 inch by 10 inch image scanned in at 300 pixels per inch:
    – 8 x 300 = 2,400 pixels 10 x 300 = 3,000 pixels
    – 2,400 pixels by 3,000 pixels = 7,200,000 pixels or 7.2 megapixels

    – At 24 bits per pixel (7,200,000 x 24)
       • = 172,800,000 bits or 21,600,000 bytes (21.6 megabytes)
       • RAM memory, video memory, disk space, bandwidth,…
 Rick Graziani graziani@cabrillo.edu                                                 27
File Compression

• Typical computer screen only has
    about 100 pixels per inch, not
    300.
•   Images still require a lot of
    memory and disk space, not to
    mention transferring images over
    the network or Internet.
•   Compression – A means to
    change the representation to use
    fewer bits to store or transmit
    information.
•   Information sent via a fax is either
    black or white, long strings of 0’s
    or long strings of 1’s.



Rick Graziani graziani@cabrillo.edu        28
Run-length encoding

• Many fax machines use run-length
    encoding.
•   Run-length encoding uses binary
    numbers to specify how long the
    first sequence (run) of 0’s is, then
    how long the following sequence of
    1’s is, then how long the following
    sequence of 0’s is, and so on.
•   Fewer bits needed than sending
    100 0’s, then 373 1’s etc.
•   Run-length encoding is a lossless
    compression scheme, meaning
    that the original representation of
    0’s and 1’s can be reconstructed
    exactly.


Rick Graziani graziani@cabrillo.edu        29
JPEG
Compression




• JPEG – Joint Photographic Experts Group
• JPEG is a common standard for compressing and storing still images.
• Our eyes are not very sensitive to small changes in hue (chrominance),
    but we are sensitive to brightness (luminance).
•   This means we can store less accurate description of the hue of the
    picture (fewer bits) and our eyes will not notice it.
•   This is a lossy compression scheme, because we have lost some
    the original representation of the image and it cannot be reconstructed
    exactly.
Rick Graziani graziani@cabrillo.edu                                           30
JPEG Compression Scheme




• With JPEG we can get 20:1 compression ratio or more, without being
     able to see a difference.
•    There are large areas of similar hues in pictures that can be lumped
     together without our noticing.
•    Because of this, when Run-length compression is used there is more
     compression because there is less variations in the hue.
Rick Graziani graziani@cabrillo.edu                                         31
RAW vs JPEG




•    http://www.youtube.com/watch?v=Qsi71MEFPB8&feature=rel
Rick ated
     Graziani graziani@cabrillo.edu                     32
MPEG Compression Scheme




• MPEG (Motion Pictures Experts Group)
• MPEG compression is similar to JPEG, but applied to movies.
      – JPEG compression is applied to each frame.
      – Then interframe coherency is used, which only records and
        transmits the “differences” between frames.
Rick Graziani graziani@cabrillo.edu                                 33
             Hexadecimal Number System



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Rick Graziani graziani@cabrillo.edu   35
Rick Graziani graziani@cabrillo.edu   36
Pixels




•   A monitors screen is divided into a grid of small unit called
    picture elements or pixels.
•   The more pixels per inch the better the resolution, the
    sharper the image.
•   All colors on the screen are a combination of red, green
    and blue (RGB), just at various intensities.


Rick Graziani graziani@cabrillo.edu                                 37
Rick Graziani graziani@cabrillo.edu   38
                                      Dreamweaver




Rick Graziani graziani@cabrillo.edu                 39
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                           Hexadecimal Number
•    With web applications like HTML (Hypertext Markup
     Language), colors are sometime described using their RGB
     color specification in hexadecimal.


 Rick Graziani graziani@cabrillo.edu                          40
Hexadecimal RED GREEN BLUE

<td rowspan="2" bgcolor="#cccc99">&nbsp;</td>


Red                           Green   Blue
cc                            cc      99

<td height="30" bgcolor="#999966"><div id="mainnav">


Red                           Green   Blue
99                            99      66

# means hexadecimal in web applications


Rick Graziani graziani@cabrillo.edu                    41
Hexadecimal Numbers

•   What are they?
•   Why do these people use them?
    – web designers
    – digital medial creators
    – computer scientists
    – networking professionals




Rick Graziani graziani@cabrillo.edu   42
Rick’s Number System Rules

•   All digits start with 0
•   A Base-n number system has n number of digits:
     – Decimal: Base-10 has 10 digits
     – Binary: Base-2 has 2 digits
     – Hexadecimal: Base-16 has 16 digits
•   The first column is always the number of 1’s
•   Each of the following columns is n times the previous
    column (n = Base-n)
     – Base 10: 10,000           1,000      100     10    1
     – Base 2:             16         8        4     2    1
     – Base 16: 65,536           4,096      256     16    1


Rick Graziani graziani@cabrillo.edu                           43
Hexadecimal Digits
Hexadecimal: 16 digits

Dec                         Hex       Dec   Hex
 0                           0         8     8
 1                           1         9     9
 2                           2        10     A
 3                           3        11     B
 4                           4        12     C
 5                           5        13     D
 6                           6        14     E
 7                           7        15     F
Rick Graziani graziani@cabrillo.edu               44
0, 1, 2, 3, 4, 5, 6, 7 ,8, 9, A, B, C, D, E, F

                                      Hexadecimal
Decimal                               16’s    1’s
  8                                            8
  9                                            9
 10                                            A
 14                                            E
 15                                            F
 16                                     1      0
Rick Graziani graziani@cabrillo.edu                 45
0, 1, 2, 3, 4, 5, 6, 7 ,8, 9, A, B, C, D, E, F

                                      Hexadecimal
Decimal                               16’s    1’s
 17                                    1       1
 20                                    1       4
 21                                    1       5
 26                                    1       A
 12                                            C
 29                                    1       D
Rick Graziani graziani@cabrillo.edu                 46
0, 1, 2, 3, 4, 5, 6, 7 ,8, 9, A, B, C, D, E, F

                                      Hexadecimal
Decimal                               16’s    1’s
 30                                    1       E
 31                                    1       F
 32                                    2       0
 33                                    2       1
 50                                    3       2
 60                                    3       C
Rick Graziani graziani@cabrillo.edu                 47
Answer these

• Rick is 53 years old in decimal. How old is Rick in Hexadecimal?
              Decimal                 16’s     1’s
                 52                      3       5
                                        48   +   4

• McLuigi went into a bar and ordered a beer. The bartender ask McLuigi
    for his ID to make sure he was old enough to order a beer (21). After
    looking at McLuigi’s ID the bartender told McLuigi he was not at least
    21. McLuigi answered, “Wrong laddie, I am exactly 21. My ID shows
    my age in Hexadecimal.”
    What age is on McLuigi’s ID in Hexadecimal?

            Decimal                   16’s     1’s
                21                       1       5
                                        16   +   5
Rick Graziani graziani@cabrillo.edu                                          48
One more

•   Rick’s mom was having her 80th birthday but she didn’t like
    the fact that she was getting so “old”. So, Rick and his
    brother Frank (the smart Physicist) decided to celebrate
    her birthday in Hexadecimal.

•   What age did it say on her birthday cake?

    Happy 5 0 th Birthday!




Rick Graziani graziani@cabrillo.edu                               49
Don’t forget why we are doing this!




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                                       Hexadecimal Number


 Rick Graziani graziani@cabrillo.edu                          50
Why Hexadecimal?

•   Hexadecimal is perfect for matching 4 bits.
•   Every combination of 4 bits can be matched with
    one hex number.
•   4 bits can be represented by 1 Hex value
•   8 bits can be represented by 2 Hex values




Rick Graziani graziani@cabrillo.edu                   51
Hexadecimal Digits
4 bits can be represented by 1 Hex value

Hexadecimal: 16 digits


Dec                     Hex           Binary   Dec   Hex   Binary
                                       8421                8421
0                          0           0000    8     8     1000
1                          1           0001    9     9     1001
2                          2           0010    10    A     1010
3                          3           0011    11    B     1011
4                          4           0100    12    C     1100
5                          5           0101    13    D     1101
6                          6           0110    14    E     1110
7                          7           0111    15    F     1111
Rick Graziani graziani@cabrillo.edu                                 52
Hexadecimal Digits
4 bits can be represented by 1 Hex value

•   Hexadecimal is perfect for matching 4 bits.
•   Every combination of 4 bits can be matched with one hex number.
•   4 bits can be represented by 1 Hex value
•   8 bits can be represented by 2 Hex values



Dec.               Hex.               Binary   Dec.   Hex.   Binary
  0                  0                  0000     8      8      1000
  1                  1                  0001     9      9      1001
  2                  2                  0010    10      A      1010
  3                  3                  0011    11      B      1011
  4                  4                  0100    12      C      1100
  5                  5                  0101    13      D      1101
  6                  6                  0110    14      E      1110
  7                  7                  0111    15      F      1111
Rick Graziani graziani@cabrillo.edu                                   53
 Converting Decimal, Hex, and Binary
Dec.    Hex.   Binary       Dec.    Hex.   Binary
  0       0      0000         8       8      1000
  1       1      0001         9       9      1001
  2       2      0010        10       A      1010
  3       3      0011        11       B      1011
  4       4      0100        12       C      1100
  5       5      0101        13       D      1101
  6       6      0110        14       E      1110
  7       7      0111        15       F      1111
-----------------------------------------------------
Dec. Hex               Binary          Dec. Hex   Binary   Dec. Hex Binary
0                                                  0010     10
      F                                            1110     12
      A                                            0000          5
      C                                            0010              1000


 Rick Graziani graziani@cabrillo.edu                                         54
 Converting Decimal, Hex, and Binary
Dec.    Hex.   Binary       Dec.    Hex.   Binary
  0       0      0000         8       8      1000
  1       1      0001         9       9      1001
  2       2      0010        10       A      1010
  3       3      0011        11       B      1011
  4       4      0100        12       C      1100
  5       5      0101        13       D      1101
  6       6      0110        14       E      1110
  7       7      0111        15       F      1111
-----------------------------------------------------
Dec. Hex               Binary          Dec. Hex   Binary   Dec. Hex Binary
0     0                0000            2     2     0010     10   A 1010
15    F                1111            14    E     1110     12   C 1100
10    A                1010            0     0     0000     5    5 0101
12    C                1100            2     2     0010     8    8 1000


 Rick Graziani graziani@cabrillo.edu                                         55
What about 8 bits?
Dec.    Hex.   Binary       Dec.    Hex.   Binary
  0       0      0000         8       8      1000
  1       1      0001         9       9      1001
  2       2      0010        10       A      1010
  3       3      0011        11       B      1011
  4       4      0100        12       C      1100
  5       5      0101        13       D      1101
  6       6      0110        14       E      1110
  7       7      0111        15       F      1111
-----------------------------------------------------

HEX                                   BINARY
2 4                                     ?

Rick Graziani graziani@cabrillo.edu                     56
What about 8 bits?
Dec.    Hex.   Binary       Dec.    Hex.   Binary
  0       0      0000         8       8      1000
  1       1      0001         9       9      1001
  2       2      0010        10       A      1010
  3       3      0011        11       B      1011
  4       4      0100        12       C      1100
  5       5      0101        13       D      1101
  6       6      0110        14       E      1110
  7       7      0111        15       F      1111
-----------------------------------------------------

HEX                                     BINARY
2 4                                   0010 0100

Rick Graziani graziani@cabrillo.edu                     57
 Using Hex for 8 bits
Dec.    Hex.   Binary       Dec.    Hex.   Binary
  0       0      0000         8       8      1000
  1       1      0001         9       9      1001
  2       2      0010        10       A      1010
  3       3      0011        11       B      1011
  4       4      0100        12       C      1100
  5       5      0101        13       D      1101
  6       6      0110        14       E      1110
  7       7      0111        15       F      1111
-----------------------------------------------------
 Hex          Binary                   Hex     Binary    Hex      Binary
 12         0001 0010                  3C                99
 AB                                    1A                00
 02                                    B4                7D
            0111 0111                        1000 1111         1111 1111
            0000 0010                        1100 1001         0101 1100

 Rick Graziani graziani@cabrillo.edu                                       58
 Using Hex for 8 bits
Dec.    Hex.   Binary       Dec.    Hex.   Binary
  0       0      0000         8       8      1000
  1       1      0001         9       9      1001
  2       2      0010        10       A      1010
  3       3      0011        11       B      1011
  4       4      0100        12       C      1100
  5       5      0101        13       D      1101
  6       6      0110        14       E      1110
  7       7      0111        15       F      1111
-----------------------------------------------------
 Hex          Binary                   Hex    Binary     Hex      Binary
 12         0001 0010                  3C    0011 1100   99    1001 1001
 AB         1010 1011                  1A    0001 1010   00    0000 0000
 02         0000 0010                  B4    1011 0100   7D    0111 1101
 77         0111 0111                  8F    1000 1111   FF    1111 1111
 02         0000 0010                  C9    1100 1001   5C    0101 1100

 Rick Graziani graziani@cabrillo.edu                                       59
So why is Rick torturing us?




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                                       Hexadecimal Number


 Rick Graziani graziani@cabrillo.edu                          60
How much RED GREEN BLUE ?




<td rowspan="2" bgcolor="#cccc99">&nbsp;</td>
     Red       Green     Blue
     cc        cc        99

<td height="30"bgcolor="#999966"><divid…>
    Red        Green     Blue
    99         99        66

Rick Graziani graziani@cabrillo.edu             61
Hexadecimal # RED GREEN BLUE

<td rowspan="2" bgcolor="#cccc99">&nbsp;</td>
     Red       Green     Blue
     cc        cc        99

Convert to Binary
        Red                                    Green              Blue
Hex      cc                                      cc               99
Bin   1100 1100                               1100 1100        1001 1001



                                      24 bits represent a single color

Rick Graziani graziani@cabrillo.edu                                        62
                   Red                        Green                 Blue
Hex                 cc                          cc                  99
Bin              1100 1100                   1100 1100           1001 1001




                                      24 bits represent a single color




Rick Graziani graziani@cabrillo.edu                                          63
                     Red                   Green         Blue
Hex                 00->FF                00->FF        00->FF

Bin              0000 0000                0000 0000    0000 0000
                    thru                     thru         thru
                 1111 1111                1111 1111    1111 1111

Dec                 0 -> 255                0 -> 255    0 -> 255


255                                   255              255


                           ?                    ?            ?
 0                                    0                0

Rick Graziani graziani@cabrillo.edu                                64
255


                        ?
0

255


                       ?
0

255

                                      How Much?
                      ?               0 to 255
0
Rick Graziani graziani@cabrillo.edu               65
                   Red                      Green            Blue
Hex                 cc                        cc             99
Bin              1100 1100                 1100 1100      1001 1001


                                            Hexadecimal
Decimal                                  16’s     1’s
                                          c        c
                                              or
                                         12        12
                                       (12x16) (12x1)
  204                                 = 192 +      12



Rick Graziani graziani@cabrillo.edu                                   66
                   Red                 Green         Blue
Hex                 cc                   cc          99
Bin              1100 1100            1100 1100   1001 1001

Dec                    204              204          153




Rick Graziani graziani@cabrillo.edu                           67
255


                 204
0

255


                 204
0

255


                 153
0
Rick Graziani graziani@cabrillo.edu   68
<td rowspan="2" bgcolor="#cccc99">&nbsp;</td>




Rick Graziani graziani@cabrillo.edu             69
www.december.com




 •    For those of you interested in Web Design and Digital
      Media, you will work with colors based on hexadecimal
      code, hue, other codes, or shades.
 •    http://www.december.com/html/spec/color.html

  Rick Graziani graziani@cabrillo.edu                         70
Chili
Powder
#C73F17



 C                     7               3      F      1       7

16’s     1’s                          16’s     1’s   16’s    1’s
 12      7                             3       15     1      7
12x16 7x1                             3x16    15x1   1x16   7x1
 192 + 7                              48 +     15     16 + 7
     199                                   63             23

Rick Graziani graziani@cabrillo.edu                                71
 Chili
 Powder
#C73F17




 C7 3F 17
199 63 23


 Rick Graziani graziani@cabrillo.edu   72
Deleted the next two slides for you enjoyment.




Rick Graziani graziani@cabrillo.edu              73
Color Codes




Rick Graziani graziani@cabrillo.edu   74
Digitizing Sound
Theme from Shaft




Rick Graziani graziani@cabrillo.edu   76
Digitizing Sound




• Many definitions of analog.
• (Our definition) analog wave is a wave form analogous to the human
    voice.
•   The telephone systems uses an analog wave to transmit your voice
    over the telephone line to their Central Office.


Rick Graziani graziani@cabrillo.edu                                    77
Digitizing Sound




• Two parts of the wave:
     – Amplitude – Height of the wave which equates to volume.
     – Frequency – Number of waves per second, which equates to pitch.
•   Computers are digital devices, so the analog wave needs to be
    converted to a digital format.



Rick Graziani graziani@cabrillo.edu                                  78
Digitizing Sound




• Converting Analog to Digital requires three steps:
    1. Sampling
    2. Quantifying
    3. Coding




Rick Graziani graziani@cabrillo.edu                    79
Digitizing Sound




• Sampling – To take measurements at regular intervals.
• The more samples you take, the more accurately you represent the
    original wave, and the more accurately you can reproduce the original
    wave.




Rick Graziani graziani@cabrillo.edu                                         80
Digitizing Sound




                                      1 second, 40,000 samples
• Nyquist’s Theorem which states that a sampling of two times the
    highest allowable frequency is sufficient for reconstructing an analog
    wave into a digital data.
•   Human can hear frequencies up to about 20,000 Hz or 20,000
    frequencies per second.
•   Using Nyquist’s Theorem, this means we need to sample each analog
    wave at 40,000 times per second of sound.
•   In other words, each one second of sound gets sample 40,000 times.
    (Actually, 44,100 times per second.)
Rick Graziani graziani@cabrillo.edu                                          81
Digitizing Sound




• Quantifying – This is the process of giving a value to each of the
    samples taken.
•   The larger the range of numbers, the more detailed or specific you can
    be in your quantifying.


Rick Graziani graziani@cabrillo.edu                                          82
Digitizing Sound




• Coding – This is the process taking the value quantified and
    representing it as a binary number.
•   Audio CDs use 16 bits for coding.
•   16 bits gives a range from 0 to 65,536.
•   Actually:
     – 15 bits are used for the range of numbers
     – 1 bit is used for + (positive) or – (negative)
•   32,768 positive values and 32,768 negative values
•   How many bits does it take to record one minute of digital audio?
Rick Graziani graziani@cabrillo.edu                                     83
Digitizing Sound

•   How many bits does it take to record one minute of digital audio?
•   1 minute = 60 seconds
•   44,100 samples per second
•   This equals 2,646,000 samples.

• Each sample requires 16 bits.
• 2,646,000 samples times 16 bits per sample equals 42,336,000 bits.
• 42,336,000 bits times 2 for stereo equals 84,672,000 bits for 1 minute
    of audio.

• 84,672,000 bits divided by 8 bits per byte equals 10,584,000 bytes for
    1 minute of audio. (More than 10 megabytes!)

• One hour of audio equals 635,040,000 bytes or 635 MB (megabytes)!

Rick Graziani graziani@cabrillo.edu                                        84
MP3 Compression




• Compressing digital audio means to reduce the number of bits needed
    to represent the information.
•   There are many sounds, frequencies, that the human ear cannot hear,
    some too high, some too low.
•   These waves can be removed without impacting the quality of the
    audio.
•   MP3 uses this sort of compression for a typical compression ratio of
    10:1, so a one minute of MP3 music takes 1 megabyte instead of 10
    megabytes.

Rick Graziani graziani@cabrillo.edu                                        85
Suggested music for your enjoyment…




• Couple of the first concerts I ever went to…




Rick Graziani graziani@cabrillo.edu              86
Advantage of Digitizing Information




• A key advantage to digital representation of information,
    images and sounds, is that the it can be reproduced
    exactly without losing a “bit” of the quality.




Rick Graziani graziani@cabrillo.edu                           87
   Data Storage – Part 2

CS 1 Introduction to Computers and Computer
                 Technology
                Rick Graziani
                   Fall 2010

								
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