Learn in the textbookDigital Representation of Audio and File Formats
DefinitionPCM (Pulse Code Modulation) is a method that processes an analog sound wave through sampling, quantization, and encoding, in that order, turning it into a sequence of 0s and 1s.
ExplanationSampling reads the height of the wave at fixed time intervals, quantization rounds each reading to one of a fixed set of levels, and encoding writes those numbers as 0s and 1s. Raising the number of samples per second (sampling frequency, 標本化周波数) and the number of bits used to express the levels (quantization bit depth, 量子化ビット数) brings the result closer to the original wave, but also increases the data size. The data size equals sampling frequency × bit depth × channels × seconds, so recording 10 seconds at 8,000 samples per second, 8 bits, and 1 channel gives 640,000 bits (80,000 bytes).
AnalogyIt is like taking burst photos of a runner at fixed intervals, reading each position off the nearest mark on a scale, and writing it down as a number.
Memory hookRemember the order as three actions: measure → round → write. The C in the name (Code) matches the last step, encoding.