#11 Jun 2022 Q6(a)(i) 3 marks 1.2.4 sound sampling

Question

Lead-in: A student records a podcast about computer science.

(a)(i) Describe how an analogue sound wave is converted into digital form.

[3]

Why this question is tricky

A common misunderstanding is that the wave frequency is used. The frequency in sound sampling is the number of samples taken each second... It is not the number of changes in a second that is recording, it is the height of the wave.— J277_01_ER_Jun2022.txt lines 327-331

MS complexity 4/10: Explicit MS exclusion — "MP2 do not award frequency of the wave is measured". Same trap recurs in Jun24 Q5(a)(i).

Full-marks model answer

The analogue sound wave is sampled — the amplitude (height) of the wave is measured at set/regular time intervals.

Each sample/measurement is converted into a binary number, and the binary numbers are stored sequentially.

Mark allocation (3 marks — any three of)
  • MP1: "(analogue) sound wave is sampled".
  • MP2: "amplitude / height (of wave) is measured" — not "frequency".
  • MP3: "at set/regular time intervals (or by example)".
  • MP4: "Each sample/measurement is stored as a binary number".
  • MP5: "The binary number for each sample is stored sequentially".

Watch out for...

The amplitude (height) of the wave is what is measured. Never write "the frequency of the wave is measured" — the MS explicitly excludes this. "Sample rate" is measured in Hertz, which is different from the wave's frequency. Use amplitude or height.