Pulse Code Modulation (PCM) is the fundamental process used to convert an analog signal into a digital binary sequence of 1s and 0s. This technique represents the message signal in a discrete form in both time and amplitude, making it truly digital.

The PCM process in a transmitter involves three fundamental operations:

1. Sampling: This first step collects data points at instantaneous values of the analog message signal. It’s like taking a series of “snapshots” of the signal at regular, discrete intervals of time.
2. Quantizing: After sampling, there can be an excessive number of bits representing the different signal levels. Quantizing simplifies this by rounding off the sample values to a finite, predefined set of levels. This reduces redundant information and compresses the data.
3. Encoding: In the final step, a unique binary code (a sequence of 1s and 0s) is assigned to each of the quantized levels. The output is a stream of binary data that represents the original analog signal.

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Once we have a digital signal in the form of binary 1s and 0s, we need a way to transmit it. This is where digital modulation techniques come into play.