Speech coding in DMR, D-STAR and System Fusion

Example of a speech signal which transitions
from an unvoiced to a voiced sound

Digital VHF and UHF communications is increasingly popular among radio amateurs using DMR, D-STAR and System Fusion. Very few radio amateurs, however, have much understanding of the signal processing required to compress a speech signal so it can be transmitted with the low bit rates available. Here is an attempt at an explanation.