Data Representation · 3 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 5% of your exam marks.
ASCII/Unicode, sound sampling and pixel/colour depth appear regularly as 2 to 4 mark questions.
The standard exam formula for the size of an uncompressed sound file is:
file size (bits) = sample rate × sample resolution × duration
where:
To convert to bytes, divide by 8 (since 1 byte = 8 bits). To convert to kilobytes, divide by 8000 (or 8192 if the question uses the binary definition of a kilobyte).
Example — A 5-second sound clip is recorded with a sample rate of 8000 Hz and a sample resolution of 16 bits. Calculate the file size in bytes.
Example — A 30-second recording at 44 100 Hz and 16 bits is compared with the same recording at 22 050 Hz and 8 bits. How much smaller is the lower-quality version?
This makes sense: halving the sample rate halves the file size, and halving the sample resolution halves it again, giving a factor of 4 overall.
Common slip: forgetting to divide by 8 at the end. If the question asks for bytes, kilobytes or megabytes, you must divide; if it asks for bits, you do not.