Making a sound file smaller

National 5 Computing Science: Web design and development

"A sound file on a web page takes too long to load. How could it be made smaller?" The examiners' reports for 2023 and 2025 say many answers to questions like this talk about images instead of sound, or say only "compress it".

What makes a sound file big

A recording is stored as thousands of samples every second. The sampling rate is how many samples are taken each second. More samples means better quality, and a bigger file.

Ways to make it smaller (and still the same length)

Reduce the sampling rate. Fewer samples each second, so less data. The sound quality drops a little.
Use a compressed format, or compress it further. A WAV file is not compressed; saving it as MP3 makes it much smaller. An MP3 can be saved again at a lower quality setting to compress it further.

WAV and MP3

	WAV	MP3
Compression	None	Compressed (lossy: some data is removed for good)
Quality	High	Lower: some detail is lost
File size	Large: slow to load	Small: quicker to load

What does not gain the mark

"Reduce the resolution." (Resolution is for images, not sound.)
"Compress it." (Only if the answer makes clear the file is compressed further, for example a lower-quality MP3.)
"Make the clip shorter." (The question usually says it must stay the same length.)

For an image file, the answers are different: reduce the resolution or the colour depth, or use a compressed format such as JPEG.

Try two exam-style questions

Choose an answer, say how sure you are, then press Check. Every wrong answer tells you why it is wrong.

The File formats lab simulation — **In the course: File formats lab.** Change the resolution, colour depth and sampling rate of real files and watch the quality and the file size change.

The full course covers every topic like this. Every topic in National 5 Computing Science has a short note, a simulation to try and a practice quiz with feedback on every answer, plus coding lessons, a full mock exam and a progress report for parents.

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This site is independent: it is not connected to the SQA or Qualifications Scotland. Points from the examiners' course reports are given in our own words.