= Separable distortion
{title2=$\bar d(x^n,\hat x^n)=n^{-1}\sum_{i=1}^n d(x_i,\hat x_i)$}
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.<6.441 Information Theory (Spring 2016 lecture notes) by Yury Polyanskiy and others/Chapter 23: Rate-Distortion Theory>[§23.2, Definition 23.1, printed pp. 242–243]{ref}
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