ITPEC FE Morning October 2023 Question 24

Sampling — the PCM step that measures the analog signal at fixed time intervals.

PCM (pulse code modulation) digitises audio in three steps, in this order:

1. Sampling: read the analog amplitude at a regular interval, for example 44,100 times a second
2. Quantization: round each sampled amplitude to the nearest of a fixed number of levels
3. Encoding: write each level as a binary code

Capturing values at a regular interval is the first step, sampling.

Answer (d)

Why not others:

• •(a) Encoding — the last step, turning the quantized levels into bits; it captures nothing from the signal
• •(b) Reverse quantization — belongs to playback, mapping stored levels back to amplitudes
• •(c) Quantization — rounds values that sampling has already captured; it divides the amplitude, not the time

Key rule: In PCM, sampling slices time, quantization slices amplitude, and encoding turns the result into bits.

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