Comparison of PCM codes for direct recording

The bit packing performance of randomized-non-return-to-zero, odd parity-non-return-to-zero, delay modulation, and bi-phase in direct recording was experimentally compared at a bit error probability (BEP) of 10 to the -6th. The effect of bit patterns, record and reproduce levels, bias level, tape speed, tape recorder bandwidth, bit synchronizers, and crossplay between tape recorders on bit packing density was investigated. At high bit packing densities, significant variations in data quality were found for changes in these parameters. This imposes limitations on practical bit packing densities. Some bit synchronizers were found to seriously reduce bit packing densities.