Q.P., an improved code for high density digital recording

This paper describes a new digital recording code format, Quadra-Phase (QP), designed for high density applications. QP is well suited for use on bandpass channels, such as a tape recorder channel, because its frequency response spectra matches the recording channel. This code is described and compared with other common PCM codes. The encoding and decoding processes are presented, and eye-patterns and spectra of QP and other codes are shown. QP achieves the same packing performance as NRZ, without the need for very low frequency channel response.