Digitization is the process of converting analog data into digital signal. Digitizing speech was a project first undertaken by the Bell System in the 1950s. The original purpose of digitizing speech was to deploy more voice circuits with a smaller number of wires. This evolved into the T1 and E1 transmission methods of today. A great example is the telephone system. The human voice ↔ analog data ↔ analog signal. The analog signal is sensitive to noise, especially over long distance and cannot be perfectly reconstructed. In order for this to work , the digitize the analog signal at the sender, then transmit digital signal and then convert digital signal back to analog data at the receiver. Quantization is the process of converting the height of the obtained samples to a finite number of discrete values. There are several methods to quantify that we will explained according to its complexity. It is necessary to use a finite number of discrete values to represent approximately the amplitude of the samples. All the amplitude range that the samples can take are divided in an equal number of intervals. A band limited signal s(t) with bandwidth ∆ν can be uniquely represented by a time series obtained by periodically sampling s(t) at a frequency fs (the sampling frequency) which is greater than a critical frequency 2∆ν. The two main encoding laws used nowadays are A law (a-law) and µ law (u-law), that are also known as g.711 codec. A Law (a-law) is used mainly in European PCM systems , and the µ law (u-law) is used in American PCM systems.