analog and digital data skills: none it concepts: analog to digital conversion, digital to analog...
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Analog and digital data
Skills: none
IT concepts: analog to digital conversion, digital to analog conversion, sample rate, sample size, quality-file size trade off
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Where does this topic fit?
• Internet concepts– Applications– Technology– Implications
• Internet skills– Application development– Content creation
Start clocks
Digital and analog clocks
Which clock is digital? Which analog?
Which clock is the closest analog to the physical world?
12:00:0012:00:0112:00:0212:00:03
etc.
A digital clock
Digital data is discreet and jumpy, not smooth and continuous
Light levelPressureSound wavesAccelerationPosition of a knobOrientation ProximityGasses in the airMagnetic field
Physical sensors → electric signals
For example, a microphone
Sound waves Varying voltage
Analog to digital converter
Computer
Computers require digital data
10010110 (150)11001001 (201)11000111 (199)…
Analog data Digital data
The input is continuous, analog data
Sample the signal at regular intervals
S1 S2 S3 . . .
v1
v2
v7
S7 . . .
Each sample produces a number
v1
v2
v9
Each sample produces a number
v1
v2
v9
A jagged approximation of the original, continuous signal
More frequent sampling results in a better fit
Each sample produces a number
But
How big (how many bits) is each number?
What time is it between seconds?
Round off to the nearest second
60 steps
12 steps
4 steps
More steps (higher resolution) means smaller round-off errors
4
3
2
1
0
5
3.6
2.2
Digitizing introduces round-off errors
More steps (intervals) between the minimum and maximum values means smaller round-off errors
0
0
0
3
7
15
Number of bits Number of possible steps
1 2
2 4
3 8
4 16
5 32
…
More bits per sample → more possible steps
The quality/file size tradeoff
Increase sample rate → quality ↑ file size ↑
Increase sample size → quality ↑ file size ↑
Digital to analog converter
Computer
10010110 (150)11001001 (201)11000111 (199)…
Computers can output analog data
Generate a somewhat jagged analog signal by approximating the value between samples with straight lines
v1
v2
v9
SoundLightFlow rateTemperatureTurn things on and off
Electric signals → change physical world
A few questions
S1 S2 S3 . . .
v1
v2
v7
S7 . . .
The value of sample 9 would be between the values of which two samples?
Without looking back, what two factors determine the quality or goodness of fit of a digitized signal to the original analog signal?
Where does this topic fit?
• Internet concepts– Applications– Technology (electronics)– Implications
• Internet skills– Application development– Content creation
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