Each sample of a sound wave is stored as a binary number.
Explain how increasing the bit depth affects the representation of a sound wave.
Mark scheme
Award up to two marks for a linked explanation such as:
- Each sample is stored using more bits (1) so the amplitude can be recorded more precisely (1)
- More different amplitude values can be represented (1) because each extra bit doubles the number of possible values (1)
- The height of the wave at each sample point is measured more accurately (1) so the digital wave is closer to the analogue wave (1)
- The gap between the true amplitude and the stored value is smaller (1) because there are more values for the sample to be rounded to (1)
For both marks, the expansion must follow/associate with the statement.
Do not accept 'the sound is sampled more often' or 'more samples are taken per second', as these describe the sample rate, not the bit depth.
Do not accept 'the file size increases' on its own as an effect on the representation of the sound.
Example answers and how they were marked
Each sample is stored using more bits, so the amplitude at each sample point can be recorded more precisely.
Why: Point (more bits per sample) (1) with linked reason (amplitude recorded more precisely) (1).
Each sample is stored using more bits.
Why: Creditworthy point (1) but no linked effect on the accuracy of the representation, so only one mark.
It takes more samples every second, so the wave is stored in more detail.
Why: Confuses bit depth with sample rate, so no mark is awarded.