In digital transmission of speech, audio, images and video signals residual redundancy is often left after source coding due to the complexity and delay constraints. This redundancy remains both inside one block or frame but also in a time correlation of subsequent frames. We describe an approach to improve channel and source decoding by using both kinds of correlation. Further on we consider the bit-mapping in coding and its effect on decoding. The mutual information as measurement for the gain in decoding through a priori information is explained. For better comparison and understanding, simple Gaussian distributed and time correlated parameters are used. As quality measurement the bit error rate and the parameter SNR (signal to noise ratio) are used.