The covariance matrix of vocoder speech

W. R. Crowther and C. Rader have found an efficient linear encoding for vocoder chanels which uses the Hadamard matrix. Minimization of expected mean square error leads to the conjecture that the Hadamard matrix diagonalizes the covariance matrix of the logarithm of 16 vocoder channels. The resulting covariance matrix has been computed for different choices of characteristic values.