假设模拟信号的最高频率为 10MHz，采样频率必须大于（），得到的样本信号才能不失真。
- A.5MHz
- B.10MHz
- C.15MHz
- D.20MHz
正确答案及解析
正确答案
解析
最常用的编码技术是脉冲编码调制技术（PCM），简称为脉码调制。关于PCM原理中有以下几个关键知识点：
（1）PCM要经过取样、量化、编码三个步骤。
（2）根据尼奎斯特取样定理，采样速率应大于模拟信号的最高频率的2倍。我们都知道44KHz的音乐让人感觉到最保真，这是因为人耳可识别的最高频率约为22KHz，因此当采样率达到44KHz就可以得到最满意的效果。
（3）量化是将样本的连续值转成离散值，采用的方法类似于求圆周长时，用内切正多边形的方法。而平时，我们说8位、16位的声音，指的就是28、216位量化。
（4）编码就是将量化后的样本值变成相应的二进制代码。
因此，要得到的样本信号不失真，需保证采样频率大于最高频率的两倍，即20MHz。
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