Low-rate tree coding of autoregressive sources (Corresp.)

The performance of differential pulse-code modulation and random codes is evaluated experimentally for a range of autoregressive sources, including Gaussian and Laplacian sources of orders
1, 2
, and
3
encoded at rates
1, 2
, and
7
. Correlations are typical of those encountered in speech and images. Results show that the gain from a fixed moderate degree of code searching increases as the rate decreases, and increases consistently with
1 /D_{o}
, where
D_{o}
is the Berger-Gray critical distortion. Laplacian and Gaussian sources behave similarly. Random codes perform better than DPCM codes for lightly correlated Laplacian sources but are otherwise worse.