说明：  PCM是Pulse code modulation的缩写，它是对波形最直接的编码方式。它在音频中的地位可能和BMP在图片中的地位有点类似吧
(Pulse code modulation PCM is the abbreviation, it is the most direct waveform coding. It' s position in the audio may be the status of BMP in the picture is somewhat similar to it)