ANALOG AND DIGITAL MEDIA: DIGITIZATION

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Rev 01/01/2015

Analog versus digital

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

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Analog: Infinite subdivisions

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

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Analog InformationContinuous; Digital Discrete

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

Digital Media Examples

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,…

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Example: Sound-Analog

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

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Analog to digital example

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

Digitization: In GeneralConverting analog to digital Sample/measure at a given rate sample

rate , determine the associated value Convert the value into binary (0,1):

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Sound

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

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Digitization: More detailed

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

sample (process called quantizing)

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Pulse Code Modulation: … Analog to Digital

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

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PCM example 2

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Technically ½ a cycleThe 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: 00000000 00000011 00000110 00001000 00001010 00001011 00001100 00001100 00001100 00001011 00001010 00001000 00000110 00000100 00000000.

Another Example

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1 Hz

Sample Size (Audio) aka bit depth

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 0-10

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To improve the quality of the result

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Increase the bit depth Conceptually:

Audio Sampling Rate 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:

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Sample Size and Rate: CDs

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

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Common Highest frequencies in Hz

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

And

http://www.youtube.com/watch?v=qNf9nzvnd1k 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

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Home Theater

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

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REVIEW QUESTIONS

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Review Question

Digital data is _____ and analog information is _____.

A. continuous; discreteB. discrete; continuous

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Review Question

Digitization means converting _____ into _____.

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Review Question

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

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Review Question

Which of the following refers to the number of allowable levels of digitized data?

A. sampling rateB. bit depth

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Review Question

Which of the following can reduce file size of digital media? (More than one choice)

A. decrease sampling rateB. increase sampling rateC. decrease bit depthD. increase big depth

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Exercise

As a group, answer the questions re digitzation

Two teams Each team do the questions

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