In several communication fields such as, for example, the digital speech storage field, it is desirable to store a large number of complex waveforms in a digital format. Typically, waveforms of this nature are stored by storing the digitized amplitude values of successive samples of the waveform in accordance with well-known pulse code modulation (PCM) techniques.
A disadvantage of this type of digital storage is that each sample usually requires a minimum of 8 bits of memory space. Inasmuch as the storage of a large number of waveforms thus consumes an appreciable amount of memory, it is highly desirable for microcomputer applications to reduce these memory requirements by some form of compaction of the sample information.
Various methods for achieving this compaction, such as delta pulse code modulation (DPCM) have been proposed, but these methods save at best one or two bits per sample.