Analogue vs Digital · Sampling Rate · Bit Depth · File Size
CSZoneCambridge IGCSE Computer Science 0478
Analogue to Digital
How Sound is Stored
Sound is an analogue wave — continuous and varying. To store it digitally, a microphone measures (samples) the amplitude of the wave at regular intervals. Each sample is stored as a binary number.
Sampling rate: number of samples taken per second (Hz). Higher = better quality, more data
Bit depth: number of bits used per sample. Higher bit depth = more accurate amplitude values
The Nyquist theorem states that to accurately reproduce a sound, the sampling rate must be at least twice the highest frequency in the sound. Human hearing: up to 20 kHz, so ≥40 kHz needed — hence CD rate of 44.1 kHz.
Too low a sampling rate → aliasing — the reconstructed sound sounds different from the original
Cambridge 0478: understand how sampling rate and bit depth affect quality and file size
Exam Practice
Have a go at this question
Cambridge IGCSE 0478 style
Explain why increasing the sampling rate improves sound quality but also increases file size.
4 marks
More samples are taken per second [1] so the digital representation more closely matches the original analogue wave [1]. More samples means more data points stored [1] so the file requires more storage space [1].
Key Takeaways
What to Remember
Sound is analogue; it's sampled at regular intervals to create a digital file