AQA · GCSE · Computer Science
Course version: 8525 · Version from Sept 2020
Representing sound: Sample resolution is the number of bits per sample.
Sound is captured by sampling the amplitude of a waveform at regular time intervals.
Checked against the AQA 8525 specification (opens in a new tab) on .
- Point 7 of 12
Study notes
From the checked teaching notes for this specification point.
The idea
Sound is captured by sampling the amplitude of a waveform at regular time intervals. Each captured amplitude is stored as a binary number, and the sample resolution (also called bit depth) is the number of bits used to store each one of those samples. A resolution of 8 bits gives 2⁸ = 256 possible amplitude levels per sample; 16 bits gives 2¹⁶ = 65 536 levels. More bits per sample means finer amplitude steps, so the digitised wave follows the original more closely and quantisation error is reduced, but each sample occupies more storage. Resolution is not the number of samples taken per second (that is the sampling rate, measured in hertz) and it is not the total file size.
For example: A recording at 44 100 Hz with 16-bit resolution stores 16 bits for every one of the 44 100 samples taken each second.
What earns the marks
- Sample resolution is the number of bits used to represent each individual sample.
- A resolution of n bits gives 2ⁿ possible levels, e.g. 8 bits gives 256 levels.
- Higher resolution reduces quantisation error and improves accuracy of the reproduced wave.
- Resolution is distinct from sampling rate, which is the number of samples per second in hertz.
- Increasing resolution increases the number of bits per sample and therefore the file size.
Common mistakes and how to put them right
Confusing sample resolution with sampling rate.
Put it right: Resolution is bits per sample, whereas sampling rate is samples per second measured in hertz.
Thinking resolution is the total number of samples in a file.
Put it right: It is the bits used for each single sample, not a count of samples.
Believing a higher resolution reduces file size.
Put it right: More bits per sample increases storage, it does not reduce it.
Assuming resolution is measured in hertz.
Put it right: Hertz measures sampling rate, while resolution is measured in bits.
Exam tips
- Learn the definition precisely: number of bits per sample, sometimes called bit depth.
- Link resolution to the formula 2ⁿ to work out the number of amplitude levels for a given bit depth.
- When a question mentions both hertz and bits, identify which is the sampling rate and which is the resolution before answering.
- State the effect of increasing resolution on both accuracy and file size to gain fuller credit.
Try the lesson
The start of the Representing sound: Sample resolution is the number of bits per sample. lesson, made from checked teaching notes for this specification point.
Have a go first
Which quantity does sample resolution measure in a digital sound recording?
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Representing sound: Sample resolution is the number of bits per sample.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge