a data detection circuit employing either amplitude or transition location techniques to adjust a detection threshold for following shifts in baseline of the signal being detected . in the amplitude version , the midway amplitude value between a detected succession of positive and negative peaks adjusts the detection threshold such that threshold adjustment occurs in one detection period and is used in the immediately - following detection period . in the transition - position detection , the relative location in time of successive transitions , represented by samples of the transition of a read signal , are integrated and averaged for providing detection which tracks baseline shifts . in all cases , shifting of detection threshold is always immediately adjacent the usage of a detection threshold which continually follows a shifting dc baseline of the input signal . a tracking detection threshold follows baseline shift of a distorted read signal detects zero axis crossing of the analog signal for generating a nrzi digital waveform .