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Pulse Code Modulation(PCM)
-Common technique to convert analog sinal to digital signal. 1.analog signal is sampled
2.sampled signal is quantized
3.quantized value are encoded as a stream of bits.
Sampling
-First step in pcm.
-analog signal is samples every T(s) sec where T(s) is sample interval of period.
Inverse of sample interval is Sample rate or Sample frequency,denoted as f(s)=1/T(s).
-sampling process is referred as Pulse Amplitude Modulation(PAM).
Quantization
-Second step in PCM.
-result of sampling is a series of pulses with ampli between max ampli & min ampli.
-involve following steps.
1.assume original analog signal has ampli betn Vmax & V min.
2.divide the range into L zones, each of height delta=(Vmax-Vmin)/L.
3.assign quantized value of 0 t
L-1 to the midpoint of each zone.
4.approax value of sample ampli to quantized values.
Encoding
-Thrid step in PCM.
-after each sample is quantized and no. of bits per sample is decided and each sample is changed to an n(b)-bit code word.
-no. of bits on each sample is determined by from the no. of quantization level(L).
- n(b)=log(2) L
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