1. A data processing circuit, the data processing circuit 1 comprising: a data detector circuit operable to apply a data detection algorithm to a data input to yield a detected output; a data decoder circuit operable to apply a data decode algorithm to a decode input to yield a decoded output, wherein the decode input is selectable between the detected output, and a modified version of the detected output; and a modification circuit operable to receive the detected output and to provide the modified version of the detected output, wherein the modification circuit includes a comparator circuit configured to compare the detected output with an identified pattern.