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AS · Practice questions · Sampled sound

Sample, then store.

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

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

Rate times resolution.

01
Recall
[2 marks]

Explain the terms sampling rate and sampling resolution.

  • Sampling rate: the number of samples taken per second. ✓
  • Sampling resolution: the number of bits used to store each sample. ✓
02
Explain
[3 marks]

Describe how a sound is converted into a digital form so that it can be stored by a computer.

  • A microphone produces an analogue electrical signal. ✓
  • The amplitude of the signal is measured / sampled at regular time intervals (by an ADC). ✓
  • Each sample is rounded to the nearest level and stored as a binary number using a fixed number of bits. ✓
03
Calculate
[3 marks]

A 2-minute stereo recording is sampled at 48 000 Hz with a 24-bit sampling resolution. Calculate its size in MiB, to one decimal place.

  • 48 000 × 24 × 2 channels × 120 s = 276 480 000 bits. ✓
  • ÷ 8 = 34 560 000 bytes. ✓
  • ÷ 1 048 576 = 33.0 MiB. ✓
04
Explain
[2 marks]

Explain the effect of increasing the sampling resolution of a recording.

  • More amplitude levels are available, so each sample is closer to the true amplitude and the playback is more accurate. ✓
  • Each sample uses more bits, so the file size increases. ✓
05
Calculate
[3 marks]

A mono recording at 16 000 Hz with 16-bit resolution must be no larger than 5 MiB. Calculate the maximum whole number of seconds that can be recorded.

  • 16 000 × 16 = 256 000 bits = 32 000 bytes per second. ✓
  • 5 MiB = 5 242 880 bytes. ✓
  • 5 242 880 ÷ 32 000 = 163.84, so 163 seconds. ✓
06
Analysis
[3 marks]

A podcast producer reduces the sampling rate of a speech recording from 44 100 Hz to 22 050 Hz. Discuss the effects of this change.

  • The file size halves, so it needs less storage and downloads / streams faster. ✓
  • Fewer samples per second means quick changes and high-pitched sounds are less accurately reproduced. ✓
  • For speech the drop in quality is usually acceptable. ✓

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.