Sound is converted into binary using a limited bit depth.
Describe one limitation of representing a sound sample with a limited bit depth.
Mark scheme
Award up to two marks for a linked description such as:
- Only a fixed number of amplitude values/levels can be represented (1) so the amplitude is rounded to the nearest available value/level (1)
- Fewer amplitude values/levels are available to choose from (1) so similar/close amplitudes cannot be stored as different values (1)
- The exact amplitude often falls between available values/levels (1) so the stored amplitude is not exact/less accurate (1)
Answers must relate to the number of bits per sample (bit depth) and the amplitude values/levels it can represent.
Do not accept answers about the sample rate, sample interval or the number of samples taken, or that confuse bit depth with the number of samples.
Do not award 'lower quality'/'more detail'/'less detail' unless it is linked to the number of amplitude values/levels.
Do not accept 'the sound cannot be played/stored' without a linked limitation.
Example answers and how they were marked
Only a fixed number of amplitude values can be represented, so the amplitude is rounded to the nearest available value and some detail is lost.
Why: Linked points: fixed number of amplitude values (1) and rounding to the nearest available value (1).
Only a fixed number of amplitude values can be represented.
Why: Gives the first linked point only (1); it does not develop what this limitation leads to.
A lower bit depth means fewer samples are taken, so parts of the sound are missed.
Why: Confuses bit depth with the number of samples/sample rate; no creditworthy point about amplitude values is given.