PURPOSE: To reduce data errors due to viterbi decoding by calculating a DC offset value from a signal amplitude of a test pattern of the lead of a block and setting an initial predictive amplitude value of the viterbi decoding.
CONSTITUTION: Data to be recorded and reproduced are divided into blocks in a sector unit, and the lead of each individual sector is provided with a header area. The test pattern is recorded by using 2nd and 3rd segments out of three segments of the header area at the lead of each sector. At the time of reproducing the data from the disk, a regenerative signal is inputted from a terminal 25 and is converted into a digital value by an A/D converter circuit 14, and afterward, the regenerative signal of the pattern of the 2nd header is changed over and inputted to the side of a predictive control circuit 60 by a changeover circuit 70. An offset value showing how much a DC deviation from the predictive level of the regenerative signal should exist is calculated, and is also added to a predictive amplitude value which becomes a reference, and is then inputted as the initial predictive amplitude value to a viterbi decoding circuit 50 by the circuit 60. Then, the viterbi decoding is carried out by the circuit 50 in adaptably controlling the predictive amplitude value to be inputted from the circuit 60.
HOSHINO TAKASHI
ISHII JUNICHI
