📁 Paper 1 · Topic 1: Data Representation
1.2c Representing Sound in Binary
Cambridge IGCSE Computer Science 0478 · ~10 min read · ⭐ Pro

Analogue Sound and Digital Representation

Sound is an analogue signal — a continuous wave that varies in amplitude and frequency. Computers can only store digital (binary) data, so analogue sound must be converted to digital through a process called sampling.

Sampling

Sampling is the process of measuring the amplitude (height) of a sound wave at regular time intervals. Each measurement is called a sample. Each sample is stored as a binary number.

  • Sample rate (sampling frequency): the number of samples taken per second, measured in Hertz (Hz) or kilohertz (kHz). CD quality = 44 100 Hz
  • Bit depth (sample resolution): the number of bits used to store each sample. More bits = more accurate amplitude values. CD quality = 16 bits

Effect of Sample Rate and Bit Depth

FactorHigher valueLower value
Sample rateBetter quality, more accurate sound reproduction, larger fileLower quality, fewer sound details captured, smaller file
Bit depthMore amplitude values possible, less distortion, larger fileLess accurate, more distortion (quantisation noise), smaller file

File Size Calculation

Audio file size (bits) = sample rate × bit depth × duration (seconds)

For stereo audio (2 channels): multiply by 2

Example: 30 seconds of mono audio at 44 100 Hz sample rate, 16-bit depth:

  • File size = 44 100 × 16 × 30 = 21 168 000 bits
  • = 2 646 000 bytes ≈ 2.52 MB

Analogue-to-Digital Conversion (ADC)

An ADC (Analogue-to-Digital Converter) converts analogue sound signals into digital binary data. A DAC (Digital-to-Analogue Converter) converts digital data back into analogue sound for playback through speakers.

Exam tip: Cambridge 0478 regularly asks for file size calculations for audio. Remember: size = sample rate × bit depth × time (in seconds). Then ÷8 for bytes, ÷1024 for KB. For stereo, multiply by 2.
⚠️ Common Mistakes
  • Confusing sample rate (samples per second) with bit depth (bits per sample)
  • Forgetting to multiply by duration in seconds
  • Forgetting to multiply by 2 for stereo recordings
  • Not converting bits to bytes (÷8) when asked for the answer in bytes
▶
Video coming soon
Click slide or press arrow keys to navigate
✍️

Worksheet — Sound in Binary

5 questions · 11 marks

Q1Define 'sample rate' in the context of digital audio.[2]
✅ Mark scheme
The number of samples taken [1] per second from an analogue sound signal [1]; measured in Hz or kHz
Q2Explain how increasing the bit depth improves audio quality.[2]
✅ Mark scheme
More bits per sample means more possible amplitude values [1]; so the digital recording is a more accurate representation of the original analogue sound / less distortion (quantisation noise) [1]
Q3Calculate the file size in bytes of 60 seconds of mono audio recorded at a sample rate of 22 050 Hz with a bit depth of 8 bits.[3]
✅ Mark scheme
22 050 × 8 × 60 = 10 584 000 bits [2]; ÷ 8 = 1 323 000 bytes [1]
Q4State what ADC stands for and describe its function in audio recording.[2]
✅ Mark scheme
Analogue-to-Digital Converter [1]; converts analogue sound signals into digital binary data so they can be stored in a computer [1]
Q5Explain why a higher sample rate produces a larger audio file.[2]
✅ Mark scheme
More samples are taken per second [1]; so more data (binary numbers) are stored per second, increasing the total file size [1]
Quiz — Sound
Q 1 of 8
Score
/ 8
Click to reveal
TermDefinition
🎯

Mini Test — Sound in Binary

10 minutes · 9 marks

← 1.2b Images Topic 1: Data Representation Next: 1.3 Storage & Compression →
🔒
Pro Content
Subscribe to access all lessons.
£7.99/month
or £59/year
Subscribe now →