AQA · GCSE · Computer Science
Course version: 8525 · Version from Sept 2020
Understand that sound is analogue and that it must be converted to a…
Full specification wording
Representing sound: Understand that sound is analogue and that it must be converted to a digital form for storage and processing in a computer.
Sound travels as a continuously changing wave, so a microphone produces an analogue signal that varies smoothly in amplitude over time.
Checked against the AQA 8525 specification (opens in a new tab) on .
- Point 1 of 12
Study notes
From the checked teaching notes for this specification point.
The idea
Sound travels as a continuously changing wave, so a microphone produces an analogue signal that varies smoothly in amplitude over time. Computers store and process only discrete binary values, so the analogue signal must be converted to a digital form. This is done by sampling: the amplitude is measured at regular intervals (the sample rate, in hertz) and each measurement is rounded to the nearest value allowed by the bit depth. A higher sample rate and greater bit depth give a more accurate representation but a larger file. The digital samples are stored as binary, and a digital-to-analogue converter turns them back into a wave for playback.
For example: Sampling at 44 100 Hz means 44 100 amplitude readings per second, each stored using the chosen number of bits.
What earns the marks
- States that sound is a continuous analogue wave varying in amplitude over time.
- Explains that a computer stores and processes only discrete binary (digital) data.
- Describes sampling as measuring amplitude at regular intervals at a given sample rate.
- Explains that bit depth determines how precisely each sample's amplitude is recorded.
- Recognises that higher sample rate and bit depth improve accuracy but increase file size.
- Identifies the role of an analogue-to-digital converter for capture and a digital-to-analogue converter for playback.
Common mistakes and how to put them right
Claiming a computer can store the analogue wave directly.
Put it right: Explain that the wave must be sampled and each sample stored as binary.
Confusing sample rate with bit depth.
Put it right: Sample rate is readings per second (Hz), while bit depth is bits used per sample.
Assuming higher quality is always free.
Put it right: Note that increasing sample rate or bit depth raises the file size.
Exam tips
- Use the words analogue, sample, sample rate and bit depth precisely in your answer.
- Link each conversion stage to its purpose: capture to digital for storage, digital back to analogue for playback.
- When comparing quality, state the effect on both accuracy and file size.
Try the lesson
The start of the Representing sound: Understand that sound is analogue and that it must be converted to a digital form for storage and processing in a computer. lesson, made from checked teaching notes for this specification point.
Have a go first
A microphone captures a continuous sound wave. Why must this sound be converted into digital form before a computer can store it?
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