ANALOG AND DIGITAL MEDIA: DIGITIZATION

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Rev 07/28/2015

Analog versus digital

Describe: examples, definition,?

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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 (Good representation: An analog watch), as is sound loudness

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Analog InformationContinuous; Digital Discrete

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.

Which is continuous?More accurate?Easiest to store in computers?

Digital Media Examples?

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An Analog Example: Sound

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

• Sample Rate? (approx.)

Digitization: In GeneralConverting analog to digital Sample/measure at a given 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 By moving back and forth, the speaker

increases and decreases the air pressure in front of it thus creating sound waves

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Digitization: More detailed

2-step process:1. Sample/measure at a known frequency, (Hz,

cycles/second)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 at uniform intervals, and each sample is quantized to the nearest value within a rangeExample: Assume 1Hz cycle (In real life, couldn't hear freq

that low) Sample 16 times /second… sample rate Range 0-10 …may be called the bit

depth.Graphically: 11

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.List the sample values for the first 5 samples...in decimal ?

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

For each sample determine a value (bit depth) the number of bits of information in each

sample An 8 bit depth means each sample value is

between 0 and ? 16 bit samples result in values between 0

and ?

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To improve the quality of the result

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Increase the bit depth.The more bits that are used, the more precise the representation of each sample.

2.) Increase sample rate 1.)

To improve the quality of the result

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1.) Increase the bit depth. The more bits that are used, the more precise the representation of each sample. 2.)Increase the sample rate The more often you sample the most accurate the final result

Audio Sampling Rate: More details

Let’s say we want to record (digitize) music Humans can hear sound between 20 and 20,0000 Hz To capture the sound, 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 ? cycles/second?(Google it) Therefor: what sample rate should we use if recording

voice:

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Sample Size and Rate: CDs

Sample size is 16 bits…bit depth 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 is 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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