Know that a sound can be transmitted as a digital or analogue signal.
Key Concepts
The electromagnetic (EM) spectrum covers all types of electromagnetic radiation, from radio waves to gamma rays.
Sound itself is a mechanical wave, but it can be carried over the EM spectrum by converting it into an electrical signal.
Two main methods of transmitting sound: analogue and digital.
Analogue Transmission of Sound
In analogue transmission the electrical signal varies continuously in amplitude (and sometimes frequency) in direct proportion to the pressure variations of the original sound wave.
Typical analogue carrier: AM (Amplitude Modulation) or FM (Frequency Modulation) radio.
The waveform of the transmitted signal is a smooth curve that mirrors the original sound pressure waveform.
Disadvantages: susceptible to noise and distortion; quality degrades with distance.
Digital Transmission of Sound
Digital transmission converts the continuous sound waveform into a series of discrete numbers (binary data) that can be sent over digital communication channels.
Process involves sampling, quantisation, and encoding.
Common digital carriers: CD audio, MP3 files, digital radio, Bluetooth audio, internet streaming.
Advantages: high resistance to noise, easy to store and manipulate, can be compressed.
Disadvantages: requires conversion equipment, introduces a small delay (latency).
Comparison of Analogue and Digital Signals
Aspect
Analogue
Digital
Signal Form
Continuous waveform
Discrete binary numbers
Transmission Medium
Radio waves, telephone lines (analogue modulation)
Radio waves, optical fibre, Ethernet (digital modulation)
Noise Sensitivity
High – noise adds directly to the signal
Low – noise can be filtered out by error‑checking
Bandwidth Requirement
Usually lower (depends on carrier)
Higher – depends on sampling rate and bit depth
Quality Over Distance
Degrades gradually
Remains constant (until data loss)
Typical Uses
FM/AM radio, analogue telephone
CDs, MP3, digital TV, internet audio
Sampling and Quantisation
To digitise a sound, the continuous waveform is sampled at regular intervals and each sample is assigned a numeric value (quantisation).
The minimum sampling rate required to reproduce a signal without aliasing is given by the Nyquist theorem:
\$fs \ge 2 f{\text{max}}\$
where \$fs\$ is the sampling frequency and \$f{\text{max}}\$ is the highest frequency component in the original sound.
Quantisation assigns each sample a value from a finite set of levels. The number of bits per sample determines the resolution:
Radio broadcasting – analogue (AM/FM) vs digital (DAB).
Telecommunications – analogue telephone networks vs digital mobile networks (e.g., 4G, 5G).
Audio storage – vinyl records (analogue) vs CDs/MP3s (digital).
Streaming services – rely entirely on digital encoding and transmission.
Suggested diagram: Flowchart showing the conversion of a sound wave into an analogue signal (modulation) and into a digital signal (sampling → quantisation → encoding).