2-Signalling Flashcards
What does a signal do?
A signal transfers information from one location to another.
What are the 2 ways signals can be converyed?
Through sound or light
What are digitised signals?
Signals of a string of binary digits from the sender to the reciever.
What is the number of bits required?
number of bits per character X number of characters per page X number of pages
What is 1 Byte?
8 Bits
What is an analogue signal?
Signals which vary from one value to the next without fixed values.
For most of the 20th century, what were most long distance communication systems examples of?
Analogue signals
What happens in an analogue telephone?
A sound vibration changes into matching oscillations of P.D.
What is the biggest problem with analogue signals?
The need for amplification as the signal becomes weaker
If the signal becomes distorted or ‘noisy’ what does the amplification do?
It boosts the signal and the noise.
What is the noise in relation to signals?
The random variation (the spiky parts)
What happens if you filter out the noise?
You lose a lot of detail in the signal.
What can transmit information quicker: digital signals or analogue signals?
Digital signals
What is sampling?
The process in which the signal is measured at small time intervals and turned into a digital string of binary numbers.
What is analogue to digital conversion?
When you convert varying analogue to a stream of numbers
What is the quantisisation error?
The difference between the signal value and the quantisation level.
What is the resolution of a sample?
The smallest change in P.D that can be determined.
What is the equation for resolution?
P.D range of signal / number of quantisation levels
How do you calculate the number of quantisation levels possible?
2 to the power of the number of bits
What is the resolution of a sample measured in?
Volts
What does increasing the number of quantisation levels do?
It increases the demands on data storage and transmission.
What is the equation for the maximum useful number of levels?
Total noisy signal variation / noise variation
b=log2( Vtotal/Vnoise )
When working out the maximum number of useful number levels, do you round up or down?
You round up
What is a frame rate?
The time interval between each frame