an get an understanding of how people build this device. Figure 4.35 shows that block diagram. The solid line shows how the DPCM and its decoder maintain the general predictive coder-decoder structure of Figures 4.27 and 4.28, and the dashed line shows you how the predicted value is generated. Here, the block called N-tap predictor receives X'n as input and outputs Chapter Four (4.67) It's not immediately apparent from Figure 4.35 just how the predicted value of equation (4.67) is being generated at the source coder. The source coder is creating x,4 in two steps: (1) first, it creates the value x by adding x,P to É, ; then (2) it creates the predictor value x,P using this x Symbol-to-bit Bit-to-symbol Quantizer sampler Mapper Mapper modulator, channel, demodulator K-tap Predictor K-tap Predictor Figure 4.35 DPCM and its source decoder Finally, there are a couple of details regarding the source coder that I want to briefly touch on. These are details about the sampler and the quantizer in the DPCM of Figure 4.35. First, there's the question of how fast the sampler samples. In three words, not very fast (when compared to the DM). Typically in DPCM, the sampling is at the Nyquist rate or perhaps two times the Nyquist rate; that is, the sampler is sampling at twice the maximum frequency of the input, x(t), or four times that maximum frequency. Then there is a question about the quantizer-how many allowed output levels N does it use? Typically, the quantizer operates with 8, 16, or 32 allowed output levels. 4.5 Congrats and Conclusion Congrats! The end of a (rather lengthy) chapter. To recap, and I'll be brief, we learned in detail about two parts of the source coder, the sampler and the quantizer. First, we learned about three types of samplers and saw the coolest of results: as long as you sample at (at least) two times the maximum frequency, you can get your original signal back from your samples. Then we learned about quantizers, a fancy word for an "amplitude changer"-it maps the input amplitude to one of N allow