Rev 07/28/2015
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Describe: examples, definition,?
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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 (Good representation:
An analog watch), as is sound loudness
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Which is continuous?
More accurate?
Easiest to store in computers?
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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
• Sample Rate? (approx.)
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Converting 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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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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2-step process:
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2.
Sample/measure at a known frequency, (Hz,
cycles/second)
Assign a value (called bit depth) to the sample
(process called quantizing)
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The amplitude of the analog signal is sampled at
uniform intervals, and each sample is quantized to
the nearest value within a range
Example: 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:
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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.
List the sample values for the first 5 samples...in decimal ?
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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
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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Increase the bit depth.
The more bits that are used, the more precise the representation of each
sample.
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2.) Increase sample rate
1.)
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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
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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
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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 ? cycles/second?(Google it)
Therefor: what sample rate should we use if recording
voice:
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Sample size is 16 bits…bit depth
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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 is 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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