Noise feedback structure for non-orthogonal transform coding

A disadvantage of nonorthogonal transforms is the inevitable amplification of the quantization noise during synthesis. A feedback structure can be used to compensate this amplification. We try to generalize the idea of noise feedback to the case of nonorthogonal transforms. We explore the application of nonorthogonal transforms to the coding of quasi-stationary sources for which the KLT is, strictly speaking, not defined. Transforms which maximize the coding gain for the assumed model of the quasi-stationary source are found, which are generally nonorthogonal. The proposed transforms along with the feedback structure are seen to perform better than the average KLT for AR sources and real life speech signals.