Abstract: An apparatus and method for compressing an input sequence of data items produced by sampling a periodic waveform compresses such input sequence by searching a history buffer operable to store consecutive data items, to locate a stored sequence of consecutive data items matching the input sequence. Matching is deemed to occur when each data item in the input sequence is within non-equal upper and lower limits of its corresponding data item in the stored sequence. When a stored sequence matching the input sequence is located compressed output data is produced to represent the stored sequence and the stored sequence is again stored in the history buffer to succeed the data items already stored therein. When a stored sequence matching the input sequence is not located, a representation of the first data item in the input sequence is produced and the first data item is stored in the history buffer to succeed the data items already stored therein.