For example, PCM and ADPCM belong to waveform coding, which directly quantifies each sample point of the waveform, or compresses by using the correlation between waveforms to remove redundancy, and can maintain relatively good speech quality, but the coding rate is high and the compression is small.
ADPCM is the lossy compression of LPCM data. In the compression process, the quantization parameters are small and large, and the size is adjusted according to the difference. In addition, it can predict the difference between the previous data and the later data, and try to make the difference relatively small.