An encoding data processing apparatus generates at least one water marked version of an original item of material formed by introducing one of a predetermined set of code words into a copy of the original material item. The apparatus has a bandwidth adaptation processor configured to adapt a bandwidth of the code word to at least part of a bandwidth of the original material item, and an encoder configured to combine the bandwidth adapted code word with a copy of the original material item. The probability of correctly detecting a code word is improved by combining the code word with a part of the bandwidth of the material item. As a result, if the material is transformed in some way the code word may still be detected.