Representing Sound: Sampling Rate and Bit Depth

Sound is a continuous pressure wave — a vibration that travels through air (or another medium) and arrives at the ear as smoothly varying changes in air pressure. This is an analogue signal: it can take any value within a range, and it changes continuously with no gaps.

Computers can only store and process digital data — discrete binary values with no in-between states. To store sound on a computer, the continuous analogue signal must be converted into a sequence of discrete binary numbers. This conversion process is called analogue-to-digital conversion.

Property	Analogue sound	Digital sound
Values	Continuous — any value	Discrete — fixed steps
Storage	Cannot be stored directly	Stored as binary numbers
Quality loss	None in transmission	Depends on sampling settings

The higher the quality of the digital representation, the more closely it approximates the original analogue wave — and the more storage it requires.

Sampling is the process of measuring the amplitude (loudness) of a sound wave at regular intervals and recording each measurement as a binary number.

Each individual measurement is called a sample. The sequence of samples forms a digital approximation of the original wave.

Analogue wave (continuous):
    ╭───╮       ╭───╮
───╯     ╰───╯     ╰───

Sampled (discrete measurements at fixed intervals):
  ×   ×   ×   ×   ×   ×

The accuracy of the digital representation depends on two factors:

1. How often samples are taken — the sampling rate
2. How precisely each sample is recorded — the sample resolution

A digital recording that uses many samples per second, each stored with many bits, closely matches the original wave. Fewer or less precise samples produce an approximation that loses detail.

Sampling rate is the number of samples taken per second. It is measured in hertz (Hz) or kilohertz (kHz).

A higher sampling rate captures more of the original wave's shape per second, producing a more accurate digital recording.

Sampling rate	Typical use
8,000 Hz	Telephone voice calls
22,050 Hz	Low-quality audio
44,100 Hz	CD-quality audio
96,000 Hz	Professional studio recording

Effect on quality and file size: doubling the sampling rate doubles both the accuracy of the recording and the amount of data generated per second. A 44,100 Hz recording captures 44,100 measurements every second — more than five times as many as an 8,000 Hz telephone recording.

(Extra context — not required by AQA 8525) Sampling rate must be at least twice the highest frequency present to avoid distortion. Human hearing reaches approximately 20,000 Hz, which is why CD audio uses 44,100 Hz.