ITPEC IP October 2023 Question 3
When a sound is recorded in a computer file, it is to be stored as a series of 8-bit encoded data. When the same sound source is sampled at the same sampling frequency and then encoded as a series of 16-bit data in lieu of 8-bit data, which of the following is an appropriate description concerning this encoding?
Explanation
The amplitude of the sound can be recorded more finely — the bit count per sample sets how many loudness levels each sample can take.
Sampling measures the sound's amplitude at fixed intervals (the sampling frequency); quantization stores each measurement as a number. With 8 bits a sample takes one of 28 = 256 levels; with 16 bits one of 216 = 65,536 levels. The steps are 256 times finer, so the amplitude is recorded more precisely and quantization noise falls.
Answer (a)
Why not others:
- •(b) — each sample now takes 16 bits instead of 8, so the same recording time needs twice as much data, not less
- •(c) — there is twice as much data to process, so the load does not decrease
- •(d) — the highest frequency that can be recorded is half the sampling frequency, which is unchanged here; bit depth does not affect it
Key rule: Sampling frequency decides how high a pitch can be captured; quantization bits decide how finely each sample's amplitude is measured. Raising either one increases the amount of data.
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