School of Engineering (SEN)

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PCM-Based digital audio coding & transmission over serial line
(2010) Aamir Saeed Khan; Saad Hassan
Pulse-code modulation (PCM) is a digital representation of an analog signal where the magnitude of the signal is sampled regularly at uniform intervals, then quantized to a series of symbols in a numeric (usually binary) code. The main purpose of this project is to analyze different aspects of Pulse Code Modulation including sampling theory, quantizing and effect of non-uniform quantization. "Sampling is the first step in any pulse modulation system. In fact by sampling, a signal is represented by set of discrete samples. If the frequency of the sampling is high enough, the original signal can be recovered from the samples. From the mathematical point of view, the sampling process can be considered as the multiplication of the message signal by a train of Dirac impulses.'' The sampling rate, or number of samples per second, is several times the maximum frequency of the analog waveform in cycles per second or hertz. The instantaneous amplitude of the analog signal at each sampling is rounded off to the nearest of several specific, predetermined levels. This process is called quantization. The number of levels is always a power of 2 -- for example, 8, 16, 32, or 64. These numbers can be represented by three, four, five, or six binary digits (bits) respectively. The output of a pulse code modulator is thus a series of binary numbers, each represented by some power of 2bits.