Deck 6: Signalling 2 Flashcards
The values that a digital signal can take depend on what?
- 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.
What type of signals are not limited in the values they can take?
Analogue signals are not limited in the values they can take- they vary continuously.
Why is it much easier to reconstruct a digital signal rather than an analogue signal?
- Because the number of values a digital signal can take is limited.
What is digitising?
- Transforming an analogue signal into a digital signal.
How do you digitise a signal?
- 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.
How well a digital signal matches the original signal depends on what two factors?
1) The difference between the possible values(resolution)
2) The time taken from one sample to the next(sampling rate).
How can you calculate the maximum number of bits a digitised signal can have?
Maximum number of bits = log2(Vtotal/Vnoise)
What is the sampling rate?
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.
What are the consequences of having a low sampling rate?
- A low sampling rate can create low frequency signals- called aliases - that weren’t in the original signal at all.
- Detail can be lost.
How is the minimum sampling rate calculated?
Minimum rate of sampling = 2 x maximum frequency of signal.
What are the four main advantages that digital signals have over analogue signals?
- 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.