请问为什么语音块都是20ms的？

可能是交织深度和处理时延的折中

nod。20ms语音压缩完之后，就2百个比特，都不够编一下码的，但如果更长乐，就影响语音的实时性了。

It is important to have a basic understanding of human speech, as well as Vocoder.The temporal and frequency characteristics of human sound are exploited by vocoders for speech coding.The human voice is made up of a combination of voiced and unvoiced sounds....
Although human voice is time varying,its spectrum is typically stationary over a period between 20 and 40 ms. This is the reason why most vocoders produce frames that have a duration on this order. For example,the IS-95 vocoder produces frames that are 20ms in duration.