Transcript Analog to Digital

Rev 01/01/2015
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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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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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The digital is accurate to nearest minute
Clock minute hand values are continuous.
Which is more accurate?
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HDTV
Photos shot with digital camera, or converted
from analog (using scanners)
DVD content
Really any media file on your computer:
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jpg, gif, wav, psd,…
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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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A 1Hz (cycle)
Assume x-axis (time) is one second
The red is the analog (continuous) sound
The black is the digitized sound
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Converting 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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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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2-step process:
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Sample/measure at a known frequency,
Assign a value (called bit depth) to the sample
(process called quantizing)
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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:
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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: 00000000 00000011 00000110
00001000 00001010 00001011 00001100 00001100 00001100
00001011 00001010 00001000 00000110 00000100 00000000.
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1 Hz
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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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Increase the bit depth
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Conceptually:
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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
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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 is 16 bits
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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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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
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My speakers only go down to 80Hz..were for effects speakers in home
theater…lower frequencies to sub-woofer
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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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Digital data is _____ and analog information is
_____.
A. continuous; discrete
B. discrete; continuous
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Digitization means converting _____ into _____.
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Converting from analog to digital involves a twostep process: _____ and _____.
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Which of the following refers to the number of
allowable levels of digitized data?
A. sampling rate
B. bit depth
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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
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As a group, answer the questions re digitzation
Two teams
Each team do the questions
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