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Computer Science A-Level > Section 3: Data Representation > Flashcards

Section 3: Data Representation Flashcards

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1
Q

Chapter 17:

What form do natural sound waves take?

A

Continuous, Analogue.

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2
Q

Chapter 17:

What form must sound waves be converted to, to be interpreted by a computer?

A

Discrete, Digital.

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3
Q

Chapter 17:

What does Analogue mean?

A

Analogue data is continuous and physical.

Often used to describe natural sound waves.

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4
Q

Chapter 17:

What does Digital mean?

A

Data that is stored in binary using different voltages, or different magnet polarisation.
The data stored is between two discrete time intervals.

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5
Q

Chapter 17:

How do we convert Analogue to Digital?

A

We take samples of the data at regular intervals, and use the readings.

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6
Q

Chapter 17:

How can we increase the precision of an Analogue to Digital reading?

A

By increasing the frequency that samples of the continuous wave are taken. (Increase sampling rate)

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7
Q

Chapter 17:

How can we increase the quality of an Analogue to Digital reading?

A

By increasing the audio bit depth.

This means that each sample will be more accurate to the continuous sound wave.

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8
Q

Chapter 17:

What is the standard sampling rate of a CD?

A

44,100 Hz

44.1 kHz

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9
Q

Chapter 17:

What does CD stand for?

A

Compact Disk.

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10
Q

Chapter 17:

What is another name for bit depth?

A

Sampling resolution.

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11
Q

Chapter 17:

What is another name for sampling resolution?

A

Bit depth.

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12
Q

Chapter 17:

How do you calculate sound sample size?

A

sample frequency (per second) * bits per sample (sample resolution) * length of sample (in seconds)

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13
Q

Chapter 17:

A sample of one minute is taken at a resolution of 16 bits and a frequency of 20KHz. What is the sound sample size?

A

(1 * 60) = 60 - minutes to seconds
16 - bits (in correct form)
(20 * 1000) = 20,000 - KHz to Hz

60 * 20,000 * 16 = 19,200,000 bits

19,200,000 / 8 = 2,400,000 bytes

2,400,000 / 1000 = 2,400 kilobytes

2,400 / 1000 = 2.4 megabytes

2.4MB

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14
Q

Chapter 17:

What does it mean for the sound sample size, if the sample is recorded in stereo rather than mono?

A

The sample size is doubled, as there are two channels to store.

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15
Q

Chapter 17:
A person speaks into a microphone, their voice is stored, and played through a speaker. What are the 7 stages of this event?

A
  1. Person speaks into a microphone.
  2. Signal goes through an amplifier, so that the audio can be adjusted.
  3. Signal goes through an Analogue to Digital Converter (ADC).
  4. Data from the ADC is stored in Binary.
  5. Data is sent to the Digital to Analogue Converter (DAC), where it is converted to a low voltage signal.
  6. Signal is amplified, by another amplifier, so that we would be able to hear it.
  7. Signal is outputted through the Speaker.
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16
Q

Chapter 17:

As the frequency of a sound wave increases, what happens to the pitch?

A

The pitch increases; becomes higher.

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17
Q

Chapter 17:

What happens to the frequency of a sound wave as the pitch of the sound increases?

A

The frequency increases.

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18
Q

Chapter 17:

As the frequency of a sound wave decreases, what happens to the pitch?

A

The pitch decreases; becomes deeper.

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19
Q

Chapter 17:

What happens to the frequency of a sound wave as the pitch of the sound decreases?

A

The frequency decreases.

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20
Q

Chapter 17:

What is Nyquist’s theorem?

A

In order to produce an accurate recording, the sampling rate must be at least double that of the highest frequency of the original signal.

sampling_rate >= 2 * highest_frequency

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21
Q

Chapter 17:

*When was Nyquist’s theorem stated and proved?

A

In 1928, Harry Nyquist stated his theorem.

His theory was proven in 1949 by Claude Shannon.

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22
Q

Chapter 17:
A sound with frequency 10,000 Hz is being sampled. What is the minimum sampling rate that is required in order to reproduce the original with good accuracy?

A

20,000 Hz (Nyquist’s theorem)

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23
Q

Chapter 17:

What does MIDI stand for?

A

Musical Instrument Digital Interface.

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24
Q

Chapter 17:

What does a MIDI controller do?

A

Carries Event Messages that specify pitch of a note, duration of a note, timbre, vibrato and volume changes, and synchronise tempo between multiple devices.
PDTVTV
Pitch Duration Timbre Vibrato Tempo Volume

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25
Q

Chapter 17:

What is Timbre?

A

Pronounced Tam-bru.

What is making the sound.

The shape of the sound wave.

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26
Q

Chapter 17:

What is vibrato?

A

How much a sound vibrates.

How smooth or jittery the sound wave is.

Sine wave is smooth,

y = sin(x) + ( sin(10x)/10 ) is more jittery, so would have a higher vibrato.

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27
Q

Chapter 17:

How is MIDI stored?

A

MIDI is stored as a set of instructions, rather than a live source.

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28
Q

Chapter 17:

How does a MIDI file size compare to a conventional recording of the same quality?

A

MIDI files are roughly 1000 times smaller than conventional recording.

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29
Q

Chapter 13:

What is a Natural Number?

A

Whole Number used in counting.
Positive whole Number (and 0).

0, 1, 2, 3, 4, …

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30
Q

Chapter 13:

What is an Integer Number?

A

Whole Numbers.

…, -3, -2, -1, 0, 1, 2, 3, …

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31
Q

Chapter 13:

What is a Rational Number?

A

Numbers that can be expressed as a fraction of integers.

e. g.
- 10.323, 1.0, 1.5, 2.7625

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32
Q

Chapter 13:

What is an Irrational Number?

A

Numbers that can not be expressed as a fraction of integers.

e.g.
pi, e, sqrt(2)

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33
Q

Chapter 13:

What is the Symbol for Natural Numbers?

A

N (but fancy)

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34
Q

Chapter 13:

What is the Symbol for Integer Numbers?

A

Z (but fancy)

35
Q

Chapter 13:

What is the Symbol for Rational Numbers?

A

Q (but fancy)

36
Q

Chapter 13:

What is a Real Number?

A

“The set of all real world quantities”.

All Numbers that are not imaginary, ordinal, or infinity.

37
Q

Chapter 13:

What is the Symbol for Real Numbers?

A

R (but fancy)

38
Q

Chapter 13:

What is an Ordinal Number?

A

Numbers that describe position.

e.g.
first, second, third, …

39
Q

Chapter 13:

Why is Binary used?

A

Computers are comprised of binary logic as electrical components are used and high/low voltage is more consistent than having several different levels.

40
Q

Chapter 13:

Why is Hexadecimal used?

A

Binary is used by computers.

Hexadecimal maps 4 binary digits to 1 digit so that less human mistakes are made than when handling binary.

41
Q

Chapter 14:

What is the difference between a Kilobyte and a Kibibyte?

A

1 Kilobyte = 2^10 bytes (1024)

1 Kibibyte = 10^3 bytes (1000)

42
Q

Chapter 14:

What does ASCII stand for?

A

American Standard Code for Information Interchange.

43
Q

Chapter 14:

How many bits make up every ASCII character?

A

7.

But there is an extended ASCII that is 8-bit.

44
Q

Chapter 14:

What is ‘A’ in ASCII?

A

65

45
Q

Chapter 14:

What is ‘a’ in ASCII?

A

97

46
Q

Chapter 14:

What is ‘0’ in ASCII?

A

48

47
Q

Chapter 14:

How many bits make up every Unicode character?

A

16.
“UTF-16” - Unicode Transformation Format (16 bit).

But there is a further Unicode with 32 bits.
“UTF-32”

48
Q

Chapter 14:

What are Parity Bits?

A

Another bit is added to the transmission.

In Even parity, the new bit will make it so that there are and Even number of 1s in the transmission.
Vice versa for Odd parity.

Used in Error Checking as if the received signal does not meet the parity requirement, we know an error has occurred.

49
Q

Chapter 14:

Why are Parity Bits used?

A

Error Checking.

If the number of 1s in the received transmissions does not meet the parity type (odd/even), the data has become corrupt.

50
Q

Chapter 14:

What is an alternative to Parity Bits that offers Error Correction?

A

Majority Voting.

Each bit in the transmission is duplicated (there are usually 3 bits in the new one for every bit).
On the receiving end, the transmission is split into threes and the most common bit in the three is taken.

1 1 0 1 Sender’s original
111 111 000 111 Sender’s transmission
111 101 001 101 Receiver’s transmission
1 1 0 1 Receiver’s original

51
Q

Chapter 14:

What are Checksums?

A

Error Checking

An algorithm that takes a unit of data and creates a value.
The Checksum is sent with the transmission.
The receiver can separate the checksum and create their own off of the data.
If the checksums don’t match up, an error has occurred.

52
Q

Chapter 14:

What is a Check Digit?

A

Error Checking.

A type of Checksum.
Single digit from a unit of data used in Error Checking.

53
Q

Chapter 15:

What are the rules for Binary Addition?

A

0 + 0 = 0
0 + 1 = 1
1 + 0 = 1
1 + 1 = 0, carry 1

1 + 1 + 1(carry) = 1, carry 1

54
Q

Chapter 15:

When in Binary Addition does overflow become a problem?

A

When you have a carry result from the calculation at the Most Significant Bit.

55
Q

Chapter 15:

How does Binary multiplication work?

A

By separately multiplying the first number by every digit in the second number, and taking the sum of the values.

You can multiply by a digit using logical left shift.

1001 * 101 [9 * 5]

1001     (1001 *    1) 00000     (1001 * 00) 100100     (1001 * 100)

101101 [45]

56
Q

Chapter 15:

What is an Unsigned Binary Number?

A

A Binary number that can only be positive.

57
Q

Chapter 15:
What is a Signed Binary Number?
Give an example of a Sign.

A

A Binary number that can represent negative values.

Two’s Complement is an example.

58
Q

Chapter 15:

How do you convert an Unsigned Binary Number into Two’s Complement?

A

Flip and add 1.

Invert all bits (logical bitwise not),
add 1.

1 1 1 1 1 1 01  = -3
1 1 1 1 1 1 1 0 = -2
1 1 1 1 1 1 1 1  = -1
00000000 = 0
00000001  = 1
00000010  = 2
0000001 1  = 3
59
Q

Chapter 15:

How do you find the range for a Two’s Complement Number?

A

-( 2^(n-1) ) <= x <= 2^(n-1) -1

60
Q

Chapter 16:

What is another name for a Bitmap Image?

A

A Raster Image.

61
Q

Chapter 16:

What is Pixel Resolution?

A

Width in Pixels * Height in Pixels

NOT SIZE

62
Q

Chapter 16:

What does PPI stand for?

A

Pixels Per Inch

63
Q

Chapter 16:

What does DPI stand for?

A

Dots Per Inch

64
Q

Chapter 16:

What is the difference between PPI and DPI?

A

DPI relates to the real physical world, where PPI relates to digital screens.

DPI is used in printing - ink dots per inch on the page
DPI is also used in mouse input precision - pixels cursor moves per inch mouse moved.

PPI is used in digital screens.

65
Q

Chapter 16:

What is Colour Depth?

A

The amount of different colours that can be represented in an image.

1 bit = 2^1 combinations = 2 colours
2 bits = 2^2 combinations = 4 colours
…

66
Q

Chapter 16:

What is the minimum file size of an image with resolution 1024x1024, where each colour is one of 256 colours?

A

(Exclude Metadata)

1024*1024 = 1,048,576
2^x >= 256, minimise int x -> x=8

1,048,576 * 8 =
8,388,608 bits
1,048,576 bytes
1,048.576 Kilobytes

~1.049 Megabytes

67
Q

Chapter 16:

What is Metadata?

A

Data about data.

Holds the file size, file name, date created, resolution, colour depth…

68
Q

Chapter 16:

What are Vector Graphics?

A

Instead of storing an RGB value for every pixel, you store instructions for creating shapes.

e.g.
Lines,
Circles,
Arcs,
Polygons.
69
Q

Chapter 16:

What is a Vector Drawing List?

A

Stores the syntax for shape instructions.

e.g.
Circle( centre = {x, y}, radius = r, fill = colour1, border = colour2, weight = pixels )

70
Q

Chapter 16:

What are the advantages of using Vector Graphics instead of Raster?

A

Vector images will always be sharp.

Vector images can scale without loss of data.

Vector file sizes are lower.

71
Q

Chapter 16:

What are the disadvantages of using Vector Graphics instead of Raster?

A

Vector images cannot easily replicate complicated images in the form of shapes.
This makes Vector images less viable for digital camera images as well as any other complicated image.

72
Q

Chapter 18:

Why is Compression used?

A

To allow for effectively more storage space.

73
Q

Chapter 18:

What are the 2 types of compression?

A

Lossy, and Lossless.

74
Q

Chapter 18:

What is Lossy compression?

A

File size decreases (usually more than Lossless), but details are lost.

75
Q

Chapter 18:

What is Lossless compression?

A

File size decreases (usually less than Lossy), but all details are retained.

76
Q

Chapter 18:

What are examples of Lossy compression for image and audio?

A

JPEG (image),

MP3 (audio).

77
Q

Chapter 18:

What are examples of Lossless compression for image and audio?

A

PNG (image),

WAV (audio).

78
Q

Chapter 18:

How does Lossless compression work?

A

By identifying common patterns and replacing them with smaller identifiers.

79
Q

Chapter 18:

What is Run Length Encoding?

A

Lossless Compression technique.

Preface a bit with its immediate frequency.

e.g.
11122888899999
3 1s, 2 2s, 4 8s, 5 9s
31224859

80
Q

Chapter 18:

What is Dictionary-based compression

A

Lossless Compression technique.

Assign an identifier to common words and replace the instance with the word with the identifier.

e.g.
“If this long string of text was present in this long string of text then we can take this long string of text and replace it with an identifier.”

@ = “this long string of text”
“If @ was present in @ then we can take @ and replace it with an identifier.”

81
Q

Chapter 18:

What is Encryption?

A

The transformation of a comprehensible piece of data (plaintext), into an incomprehensible form (ciphertext).

82
Q

Chapter 18:

What is the Caesar Cipher?

A

Also known as the shift cipher.

Given a fixed integer key, shift every plaintext character by that key in the alphabet, or other character system.

e.g.
key = 1
a = b, b = c, … , z = a

plaintext –> ciphertext
hello –> ifmmp

83
Q

Chapter 18:

What is a One Time Pad?

A

Used in Vernam Cipher.

An Encryption Technique that cannot be cracked.

The One Time Key must be random and the same length or longer. It must be transmitted physically to avoid interception.

84
Q

Chapter 18:

What Bitwise Operation does the Vernam Cipher use?

A

XOR.

Computer Science A-Level (12 decks)

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