The discrete cosine transform (DCT) is considered as a suboptimum transform for many practical source-coding applications. Autoregressive order 1 (AR(1)) source models are good first approximations to several natural signals. It is known that the performance of the DCT depends on the sign of the autocorrelation coefficient of the AR(1) source. The authors explain theoretically this asymmetrical performance of the DCT as well as the behavior of the modified Hermite transform (MHT) and the discrete Hadamard transform (DHT), which perform symmetrically regardless of the sign of the autocorrelation coefficient. >