Chapter 2 - Signalling Flashcards
Explain what a signal is and give two examples.
A signal transfers information from one location to another through sound or light. For example, a fire alarm or a red light. A signal can also be a stream of binary 1s and 0s.
What is an analogue signal and what is the main problem with them?
An analogue signal will vary continuously from one value to the next, without fixed values. The main problem is the need for amplification as the signal becomes weaker. If signal becomes distorted or “noisy”, amplification boosts signal and noise.
Give two advantages of digital signals over analogue signals.
It is easy to detect binary “on/off” signals even when they are weak and noisy.
They transmit information much faster than analogue signals.
What is sampling?
The process in which the displacement of a continuous (analogue) signal is measured at small time intervals and turned into a digital string of binary numbers.
What is the resolution of a sample? (in word form)
The smallest change in potential difference that can be determined.
What is the equation for the resolution of a sample?
resolution = potential difference range of signals / no. of quantisation levels
Maximum useful no. of quantisation levels =
total noisy signal variation / noise variation
Vtotal / Vnoise
log 2 (Vtotal / Vnoise) =
no. of bits
What is a sampling rate (sampling frequency)?
The number of samples taken each second
What are the two conditions to ensure an original signal can be reconstructed accurately?
- > The signal cannot contain frequencies above a certain maximum
- > Minimum sampling rate > 2 x highest frequency component
What are two problems with sampling too slowly?
- > Miss out high frequency detail in original signal
- > Creates spurious low frequencies (aliases)
What is the average maximum frequency sound the human ear can detect is…
20 Hz
What frequency should music for humans be sampled at?
Above 2 * 20 Hz = 40 Hz
–> Generally sampled at 44.1 Hz
What is the bit rate?
The rate of transmission of digital information
What is the equation for bit rate?
bit rate (bits s^-1 or Hz) = samples per second * bits per sample
