AQA · GCSE · Computer Science
Course version: 8525 · Version from Sept 2020
Calculate sound file sizes based on the sampling rate and the sample…
Full specification wording
Representing sound: Calculate sound file sizes based on the sampling rate and the sample resolution.
To calculate the size of an uncompressed sound file, multiply the sampling rate (samples per second, in hertz) by the sample resolution (bits per sample) by the number of channels (1 for mono, 2…
Checked against the AQA 8525 specification (opens in a new tab) on .
- Point 8 of 12
Study notes
From the checked teaching notes for this specification point.
The idea
To calculate the size of an uncompressed sound file, multiply the sampling rate (samples per second, in hertz) by the sample resolution (bits per sample) by the number of channels (1 for mono, 2 for stereo) by the duration in seconds. This gives the size in bits; divide by 8 to convert to bytes, and by 1 000 or 1 024 (as directed) for kilobytes. For example, 10 seconds of mono audio at 8 000 Hz with 8-bit resolution is 8 000 × 8 × 1 × 10 = 640 000 bits, which is 640 000 ÷ 8 = 80 000 bytes. Doubling the sampling rate, the resolution, the channel count or the duration doubles the file size. Keep units consistent and show each step so the method is clear.
What earns the marks
- File size in bits = sampling rate × sample resolution × number of channels × duration in seconds.
- Sampling rate is in hertz (samples per second) and resolution is in bits per sample.
- Number of channels is 1 for mono and 2 for stereo.
- Convert bits to bytes by dividing by 8, and to kilobytes by dividing by 1 000 or 1 024 as specified.
- Worked example: 8 000 Hz × 8 bits × 1 channel × 10 s = 640 000 bits = 80 000 bytes.
- Doubling any one factor (rate, resolution, channels or duration) doubles the resulting file size.
Common mistakes and how to put them right
Forgetting to multiply by the number of channels, so stereo files are calculated as if mono.
Mixing units, for example using duration in minutes while the sampling rate is per second, without converting.
Failing to convert bits to bytes, leaving the answer in bits when bytes are requested.
Multiplying the sampling rate by resolution but omitting the duration in seconds.
Exam tips
- Write the formula first, then substitute values, so method marks are visible even if arithmetic slips.
- Check the units requested (bits, bytes, kB) and convert at the end.
- Convert duration to seconds before multiplying.
- Use a calculator carefully and sanity-check that a longer or higher-quality file gives a larger answer.
Try the lesson
The start of the Representing sound: Calculate sound file sizes based on the sampling rate and the sample resolution. lesson, made from checked teaching notes for this specification point.
Have a go first
A mono sound recording is sampled 8000 times per second, and each sample is stored using 8 bits. How many bits are needed to store 1 second of this recording?
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