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Átirat

Group Members :

Joshita Reddy

Nayanika Reddy

Nirmit Maniar

Implementation

  • Practical implementation of PCM makes use of other processes which are carried out in the order:
  • Sampling
  • Quantization and
  • Encoding

Linear Pulse code modulation

Pulse code modulation

  • It is a method used to digitally represent sampled analog signals
  • In a PCM stream, the amplitude of the analog signal is sampled regularly at uniform intervals
  • Each sample is quantized to the nearest value within a range of digital steps

Applications of PCM

  • Lossless encoding of audio data in the compact disc(audio cd)
  • HDMI: Audio/video connetor interface for transmitting uncompressed digital data
  • DVD and Blu-ray standards

Modulation

  • In the diagram following, a sine-wave is sampled and quantized for PCM.
  • The vertical lines are the sampling intervals

CODE:

clc;

clear all;

close all;

t=0:0.01:5;

x=2*sinc(2*pi*t);

figure;

plot(x);

hold all;

e=uencode(x,3);

d=udecode(e,3);

plot(d);

c=compand(x,255,2,’mu/compressor’);

e1=uencode(c,3);

d1=udecode(e1,3);

ex=compand(d1,255,2,’mu/expander’);

plot(ex);

xlabel(‘time’);

ylabel(‘magnitude’);

title(‘pulse code modulation of sinc function’);

Pulse code modulation and it's applications

Why PCM?

  • The stream of pulses and non pulse streams of 1's and 0's are not easily effected by interference and noise
  • Even in the presence of noise,the presence or absence of a pulse can be easily determined
  • Also digital signals are easy to process and cheaper to implement

Clarity acc to number of bits/sample

Limitations

  • There are 2 sources of impairment implicit in any PCM system
  • Choosing the discrete value near the analog signal(quantization error)
  • There is no measurement of signal between the samples;due to the sampling theorem this results in any frequency above sampling frequency being distorted or lost completely
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