An electronic system that has a permanently variable signal.
An analogue signal is continuous, so it has these characteristics:
Continuous Signals: Represent real-world phenomena like sound, temperature, or light.
Infinite Values: Can take any value within a range, allowing for precise representation.
Example
A vinyl record is an analogue system.
The grooves on the record represent continuous sound waves, capturing every nuance of the original performance.
Note
Unlike digital signals that jump between fixed values, analogue signals can take on any value within a range: ideal for representing natural phenomena like sound, light, and temperature.
Digital Systems
Definition
Digital Systems
An electronic system that uses binary signals, i.e. 0 or 1, on or off.
A digital signal is discrete, so it has these characteristics:
Discrete Signals: Break down continuous signals into distinct steps or levels.
Binary representation: information is encoded as on/off states, which A3.4.5 develops in full.
Example
A computer processes and stores information using binary code, a digital language made up of 1s and 0s.
Every action a computer performs, from typing a document to playing a video, is broken down into these discrete binary values.
Analogy
Think of analogue signals as a smooth, continuous line and digital signals as a series of connected dots.
The line captures every detail, while the dots provide a simplified, step-by-step representation.
The Differences That Actually Matter
Analogue
Digital
Signal Representation
Continuous and smooth
Discrete and binary
Precision and Accuracy
High precision but susceptible to noise and distortion
Less precise but more accurate due to error correction and noise resistance
Storage and Transmission
Requires physical media (e.g., tapes, records)
Easily stored and transmitted electronically (e.g., CDs, cloud storage)
Processing
Limited by physical components
Highly flexible and programmable
Note
While digital systems are more common today, analogue systems are still used in applications where continuous signal representation is essential, such as in high-fidelity audio equipment.
Where Each One Wins
Analogue systems are still chosen where the smoothness of the signal is the point:
Audio Equipment: Vinyl records and analogue amplifiers for high-fidelity sound.
Instrumentation: Analogue thermometers and pressure gauges for continuous monitoring.
Digital systems dominate wherever the signal must be stored, copied or sent without degrading:
Computing: Digital processors and memory for data storage and computation.
Communication: Digital signals in smartphones and the internet for reliable transmission.
The decisive advantage of digital is that a copy is perfect.
Noise that would blur an analogue signal is simply rounded away, because a value only has to be recognised as a 0 or a 1.
Example question
A recording studio records a singer's voice, then stores the recording as a digital file so it can be streamed to listeners.
(a) Distinguish between an analogue signal and a digital signal. (2 marks)
(b) Explain why the recording is converted to digital before it is transmitted. (3 marks)
Solution
(a) Award [1] for each side of the distinction, up to [2 max]. A distinction must contrast the two, not describe only one.
An analogue signal is continuous and can take any value within a range, so it varies smoothly. [1]
A digital signal is discrete and takes only fixed values, normally the two binary states 0 and 1. [1]
(b) Award [1] for each linked point, up to [3 max].
Any transmission adds noise, and noise permanently distorts an analogue signal because every value in the range is a valid value. [1]
A digital signal only has to be recognised as a 0 or a 1, so small amounts of noise can be rounded away and the original values recovered exactly. [1]
Digital data can therefore be copied, stored and streamed without degrading, and it can also be compressed and error-checked. [1]
Credit is also available for noting the trade-off: the conversion samples the sound, so some of the original detail is discarded, which is why some listeners still prefer analogue vinyl.
Active recall
What does it mean to say an analogue signal is continuous?
How many values can a digital signal normally take, and what are they called?
Why is a digital signal more resistant to noise than an analogue one?
Name one product that still uses an analogue system, and say why.
What does a digital system give up in exchange for its robustness?
