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IGCSE · Practice questions · Representing sound: sample rate and resolution

Measure the wave.

Six original Cambridge-style questions on representing sound, with worked solutions.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Rate times resolution.

01
Explain
[3 marks]

Explain how a sound is converted into binary so that a computer can store it.

  • The sound wave is sampled. ✓
  • The amplitude (height) of the wave is measured at regular time intervals (set by the sample rate). ✓
  • Each measurement is stored as a binary number using a set number of bits (the sample resolution). ✓
02
Recall
[2 marks]

Define the terms sample rate and sample resolution.

  • Sample rate: the number of samples taken in a second. ✓
  • Sample resolution: the number of bits used to store each sample. ✓
03
Calculate
[3 marks]

A 4-second sound clip is recorded with a sample rate of 32 000 Hz and a sample resolution of 16 bits. Calculate the file size in KiB. Show your working.

  • 32 000 × 16 × 4 = 2 048 000 bits. ✓
  • 2 048 000 ÷ 8 = 256 000 bytes. ✓
  • 256 000 ÷ 1024 = 250 KiB. ✓
04
Explain
[2 marks]

Describe the effect of increasing the sample resolution on a sound file.

  • More amplitude levels can be represented, so the recording is more accurate (closer to the original sound). ✓
  • Each sample uses more bits, so the file size increases. ✓
05
Apply
[2 marks]

A recording uses 11 025 Hz and 8 bits. It is re-recorded at 22 050 Hz and 16 bits, with the same length. How many times larger is the new file? Explain.

  • The sample rate doubles, which doubles the size; the resolution doubles, which doubles it again. ✓
  • 2 × 2 = 4 times larger. ✓
06
Analysis
[2 marks]

A student says "changing the sample resolution from 8 bits to 16 bits gives twice as many amplitude levels." Explain why this is wrong.

  • 8 bits give 28 = 256 levels; 16 bits give 216 = 65 536 levels. ✓
  • That is 256 times as many levels (it is the file size that doubles). ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.