Sound pressure waves in air are the objective cause of human hearing. A transducer is a device that takes power from one system and supplies power to another system. For example, a microphone is a transducer that takes sound power and supplies electrical power. The electrical power supplied by the microphone forms an analog signal. An analog signal is continuous.
Digitization is a process that converts continuous signals into a digital form.
Sampling is the process of converting a continuous signal into a set of voltages. Quantization is the process of converting the sampled voltages into a countable set of digital values. Analog data that is converted to digital data is said to be PCM-encoded. PCM stands for pulse code modulation and is a broad term that can refer to any type of digital encoding of analog data. Figure 5.1 depicts a PCM encoder.