全国2012年7月自考通信概论试题_第4页

16.若抽样速率fS＜2fH，则会产生(      )

A.叠加失真                                                      B.混合失真

C.相对失真                                                      D.混叠失真

17.理想抽样频谱的包络是(      )

A.一条曲线                                                      B.一条水平线

C.一条垂线                                                      D.一条斜线

18.在PCM中，对于语音、图像等随机信号，量化误差是(      )

A.随机的                                                         B.固定的

C.预知的                                                         D.可计算出来的

19.在脉冲编码调制过程中，每增加一位编码位数，平均量化信噪比就提高(      )

A.9dB                                                              B.8dB

C.6dB                                                              D.3dB

20.增量调制可看成是量化电平数为2的(      )

A.PCM                                                            B.DCM

C.TCM                                                             D.DPCM