OCR J277 Mark Scheme

OCR	GCSE (9-1) Computer Science Mark Scheme J277/01: Unit 1.2 Sound

Question	Answer	Marks	Guidance
1a	The number of samples taken per second [1] OR The frequency at which the sound is sampled, measured in Hertz (Hz) [1]	1	AO1 (Knowledge) Examiner Note: Do NOT accept "The speed of the sound". It must refer to how often the measurement is taken.
1b	The number of bits available for each sample [1]	1	AO1 (Knowledge) Accept "The number of bits used to store the amplitude".
2a	Working: 3000 x 8 x 10 [1] Answer: 240,000 (bits) [1]	2	AO2 (Application) Formula: Sample Rate x Bit Depth x Duration. Answer only gets full marks. If they calculate bytes immediately (30,000), award 1 mark for working if the bits calculation is implied/shown.
2b	30,000 (bytes)	1	AO2 (Application) Divide answer to 2a by 8. Allow follow-through if 2a was incorrect.
3	The amplitude (height) of the wave is measured... [1] ...at set/regular intervals (sampling) [1] These measurements are converted into binary values [1]	3	AO1 (Knowledge) Max 3 marks. Examiner Note: Common misconception: Students often say "The frequency is measured". This is wrong. The amplitude is measured; the frequency is how often you measure it.
4a	The sound will be closer to the original (analogue) wave / more accurate [1] Because the dynamic range is increased / smaller changes in loudness can be detected [1]	2	AO1 (Knowledge) Accept "Less distortion" or "Better quality". Must link quality to the ability to record a wider range of amplitudes.
4b	The file size will increase [1] Because more bits are being used to store each individual sample [1]	2	AO1 (Knowledge) Simple logic: More bits per sample = more total bits.
5a	Reduce the Sample Rate [1] Reduce the Bit Depth [1] Reduce the Duration (length) of the podcast [1]	2	AO1 (Knowledge) Max 2 marks. Do not accept "Compress it" (excluded by question). Do not accept "Delete parts" unless linked to reducing duration.
5b	Reduced Sample Rate: The sound might lose higher frequencies / sound flat / sound less clear [2] OR Reduced Bit Depth: The sound might have less dynamic range / pick up static/noise / sound distorted [2]	2	AO2 (Application) Award 1 mark for the general idea "lower quality" and 2nd mark for specific detail (e.g., losing high pitch sounds vs general distortion).