Characteristics of overwrite-induced bit shift

Overwrite-induced bit shift was investigated on high-density helical scan tape recorders using ferrite heads and metal particle tape. A high-precision time interval (TI) counter was used to measure the transition jitter. By comparing the TI histogram of pseudorandom-data-sequence and single-tone-frequency recordings, it was found the overwrite-induced bit shift is mostly due to a low-frequency noise. Properly filtering the low-frequency content of the signal through either channel code selection or playback data detection techniques can greatly reduce the shift. Implementation of overwrite digital VTRs using DC-free Miller squared code is described