1 Rev 01/01/2015

 The main difference between analog and digital /discrete is that analog data is continuous and digital data is discrete.  We need to save media as a collection of (1,0)  Real world, mainly analog : sound, your weight, temperature, light brightness…  The process of converting analog to digital: digitizing 2

 Continuous information  An infinite number of divisions exist between any two measurements…weight now, wait a bit……weight now…the difference was continuous, not discrete (just gained a pound!!)  Time is also continuous, as is sound 3

4. The digital is accurate to nearest minute Clock minute hand values are continuous. Which is more accurate?

 HDTV  Photos shot with digital camera, or converted from analog (using scanners)  DVD content  Really any media file on your computer:  jpg, gif, wav, psd,… 5

 Number of times a sound wave repeats in a second is its frequency  Measure frequency in Cycles/second-- Hertz: Hz  Named after H. R Hertz 6

7  A 1Hz (cycle)  Assume x-axis (time) is one second  The red is the analog (continuous) sound  The black is the digitized sound

Converting analog to digital  Sample/measure at a given rate sample rate, determine the associated value  Convert the value into binary (0,1): 8

 When something vibrates to make a sound, it pushes the air towards you and pulls it away from you many times a second.. You hear both the push and the pull, because both move your ear drum.  Negative amplitude occurs when air being pulled away  Positive when air pulling inward 9

 2-step process: 1. Sample/measure at a known frequency, 2. Assign a value (called bit depth ) to the sample (process called quantizing) 10

The amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range Example: Assume  1Hz cycle  Sample 16 times /second… sample rate  Range 0-10 …may be called the bit depth Graphically: 11

12 Technically ½ a cycle The blue line is an example of the audio signal, and the jagged red line would be digital representation of that ½ cycle. The sampling values would be 0, 3, 6, 8, 10, 11, 12, 12, 12, 11, 10, 8, 6, 4, and 0 or in binary:

13 1 Hz

 The amount of computer space gathered in each sample.  The higher the number, the more precise the information, the better the sound  Usually 8-bit or 16-bit samples…each time I sample (listen) I determine a value (bit depth)  An 8 bit depth means each sample value is between 0 and 256 (2^8)  16 bit samples result in values between 0 and 65,536  In earlier example: bit depth would be

15 Increase the bit depth  Conceptually:

 Let’s say we want to record (digitize) music  Humans can hear sound between 20 and 20,0000 Hz  Would sample 44,100 times per second.  This rate is the result of Nyquist’s Rate, aka Nyquist’s rule, or Nyquist’s theorem  Sample 2 x highest frequency  Music frequency 20-20,000 Hz  Sample rate then 2 *20,000=44,000 times/second…extra 100 due to Sony  Voice range is 300-4,000 cycles/second  What sample rate should we use if recording voice: 16

 Sample size is 16 bits  2 ^ 16 = 65,536 possible values  Convert the amplitude to a value between zero and 65,636  Sample rate 44,100 Hz 17

200,000 Hz Dolphins 18,500 Highest frequency heard by average woman 17,500 Highest frequency heard by average man 4096Hz Highest note on a piano 4000 The most irritating or activating frequency (chainsaw freq) (approximate) also see also see And  Write down the value when you can no longer hear the sound  My speakers only go down to 80Hz..were for effects speakers in home theater…lower frequencies to sub-woofer 18

 Should have 3 speakers in the front  Two rear speakers  Sub woofer  (called 5.1)  Sound < 80Hz are sent to the sub  That’s why the speakers in our room only play down to 80 Hz max 19

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Digital data is _____ and analog information is _____. A. continuous; discrete B. discrete; continuous 21

Digitization means converting _____ into _____. 22

Converting from analog to digital involves a two- step process: _____ and _____. 23

Which of the following refers to the number of allowable levels of digitized data? A. sampling rate B. bit depth 24

Which of the following can reduce file size of digital media? (More than one choice) A. decrease sampling rate B. increase sampling rate C. decrease bit depth D. increase big depth 25

 As a group, answer the questions re digitzation  Two teams  Each team do the questions 26