An adaptive detector, such as a maximum a posteriori (MAP) detector for a read channel, is disclosed. In one or more embodiments, a data processing apparatus, such as a read channel digital front end, includes an equalizer configured to equalize X sample data to yield equalized Y sample data. A noise predictive filter configured to receive the equalized Y sample data yielded by the equalizer is operable to filter noise in the equalized Y sample data. A detector is configured to perform iterative data detection on the filtered equalized Y sample data. The detector is operable to program a branch metric, a variance, and a scaling factor for equalizer adaptation during a global iteration of the detector.