Edexcel GCSE Computer Science (1CP2) Exam Questions

Award one mark for any of the following up to a maximum of two marks:

• Only a limited/fixed number of amplitude values can be stored (1)
• The amplitude of each sample is rounded/approximated to the nearest value that can be stored (1)
• The recording is less accurate than the original analogue sound/does not match the analogue wave exactly (1)
• Sounds louder than the highest amplitude that can be stored are clipped/distorted (1)
• Sounds quieter than the lowest amplitude that can be stored cannot be represented/are lost (1)

Allow quantisation error/noise for the amplitude being rounded to the nearest value that can be stored, but do not award a second mark for the same idea

Allow a stated consequence as a separate mark only when it is a different point from the list, e.g. fewer amplitude values can be stored (1) so very quiet sounds are lost (1)

Do not accept 'lower quality'/'poorer sound' on its own; the answer must say the recording is less accurate than the original/does not match the analogue wave

Do not accept sample rate/sample interval/number of channels (stereo/mono), as these are not limited by the number of bits available for each sample

Do not accept remedies such as 'a larger bit depth would make it more accurate', as these do not describe a limitation

Do not accept answers about file size, compression or playback method

Do not accept a statement that repeats the stem, e.g. 'the sound is stored in binary using a fixed number of bits'

Award one mark for any of the following:

• Increase the sample rate / take more samples per second (1)
• Increase the bit depth/sample resolution / use more bits per sample (1)
• Decrease the sample interval (1)

Do not accept increase the amplitude/volume

Do not accept decrease the sample rate / increase the sample interval

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.

Award up to two marks for a linked explanation such as:

• Only a limited number of different amplitude values can be stored (1) so each sample is rounded to the nearest available value and the digital wave does not match the analogue wave exactly (1)
• The wave is continuous but only a limited set of values can be represented (1) so amplitude detail/accuracy is lost (1)
• Quiet and loud parts of the sound may be stored as the same value (1) because there are too few values to tell them apart (1)
• The range of amplitudes that can be represented is limited (1) so the loudest/quietest parts of the sound cannot be stored accurately (1)

For both marks, the expansion must follow/associate with the statement.

Do not award marks for answers that say the sound cannot be stored or heard at all.

Do not award answers about the number of samples taken/sample rate, as the number of bits limits the amplitude values, not how often the wave is sampled.

Do not accept 'lower quality'/'less accurate'/'less detail' on its own without a link to the amplitude values that can be stored/the number of bit combinations.

Do not accept 'the file size is smaller' without a link to the accuracy or the range of values that can be stored.