说明：  运用MATLAB语言，进行非均匀PCM量化编码。产生一个长度为500，按N（0，1）分布的随机变量序列。用128量化电平和μ=255的μ律非线性，画出量化器的误差和输入输出关系。
(Using MATLAB language, non-uniform quantization PCM coding. Produce a length of 500, according to the sequence of random variables N (0,1) distribution. With 128 quantization law nonlinear peaceful, draw the quantization error and input-output relationship.)