Deck 6: Signalling 2

Question 1

The values that a digital signal can take depend on what?

Answer 1

• Depend on the number of bits used.
• A one bit signal can only take the values 0 and 1.
• A one byte signal can take 256 different values.

Question 2

What type of signals are not limited in the values they can take?

Answer 2

Analogue signals are not limited in the values they can take- they vary continuously.

Question 3

Why is it much easier to reconstruct a digital signal rather than an analogue signal?

Answer 3

• Because the number of values a digital signal can take is limited.

Question 4

What is digitising?

Answer 4

• Transforming an analogue signal into a digital signal.

Question 5

How do you digitise a signal?

Answer 5

• To digitise a signal, you take the value of the signal at regular time intervals, then find the nearest digital value.
• Each digital value is represented by a binary number, so you can convert the analogue values to binary numbers.
• The digital signal will not exactly the same.

Question 6

How well a digital signal matches the original signal depends on what two factors?

Answer 6

1) The difference between the possible values(resolution)

2) The time taken from one sample to the next(sampling rate).

Question 7

How can you calculate the maximum number of bits a digitised signal can have?

Answer 7

Maximum number of bits = log2(Vtotal/Vnoise)

Question 8

What is the sampling rate?

Answer 8

When you digitise a signal, you record the value of (sample) the original signal at regular intervals. The rate at which you sample the signal is called the sampling rate.

Question 9

What are the consequences of having a low sampling rate?

Answer 9

• A low sampling rate can create low frequency signals- called aliases - that weren’t in the original signal at all.
• Detail can be lost.

Question 10

How is the minimum sampling rate calculated?

Answer 10

Minimum rate of sampling = 2 x maximum frequency of signal.

Question 11

What are the four main advantages that digital signals have over analogue signals?

Answer 11

• Digital signals can be sent, received and reproduced more easily than analogue signals because they can only take a limited number of values.
• Digital signals are resistant to the effect of noise
• Digital signals can be used to represent different kinds of information in the same way - for example, images and sounds can both be represented by a string of bits.]
• Digital signals are easy to process using computers.