Separable distortion ($\bar{d}(x^n,{\hat{x}}^n)=n^{-1}{\sum }_{i=1}^{n}d(x_i,{\hat{x}}_i)$)

For a block code, separable distortion is the average of the individual symbol costs. With Hamming distortion it is the fraction of incorrectly reconstructed symbols, rather than the unnormalized number of mismatches. This normalization makes expected distortion comparable across different block lengths.^[ref]