Topic 5 - Fundamentals of Data Representation - Representing images, sound and other data

Question 1

Define Analogue and Digital data

Answer 1

Analogue - Data is continuous and has no limits
Digital - Data is discrete and can only take particular values

Question 2

How does a digital to analogue conversion work?

Answer 2

It reads a bit pattern representing an analogue signal and outputs an alternating, analogue, electrical current

Question 3

How does an analogue to digital conversion work?

Answer 3

The analogue signal is sampled at a specific frequency at regular intervals which is stored digitally as a bit pattern

Question 4

What are the benefits of vector graphics over bitmap?

Answer 4

A vector can be scaled without losing quality and often take less storage space than bitmapped graphics

Question 5

What is the sample resolution of an digitally recorded audio wave?

Answer 5

The number of bits allocated to each sample

Question 6

What is the equation for the size of a sound sample?

Answer 6

duration of the sample in seconds x the sampling rate in Hertz x the sample resolution

Question 7

What is Nyquist’s Theorem?

Answer 7

The sampling rate of a digital audio file must be at least twice the frequency of the sound to be accurately represented

Question 8

How are MIDI recordings stored?

Answer 8

A series of event messages, each representing an event in a piece of music

Question 9

What information could event messages contain?

Answer 9

The duration of a note
The instrument
The volume

Question 10

Explain the conditions required to create a Vernam cipher

Answer 10

The key must only be used once and random

Question 11

What is the process of encryption using a Vernam cipher?

Answer 11

1. Align the characters of the plaintext and the key
2. Convert each character to binary
3. Applying a XOR operation to both bit patterns
4. Converting the results back to characters