The two-dimensional discrete cosine transform applied to speech data

A two-dimensional discrete cosine transform (2-D DCT), often used for image coding, has been applied to sequences of speech spectra produced by the maximum likelihood method (MLM). The coded data was compressed by nearly 90%, reducing it to a size smaller than that needed to store the coefficients of a 10th order linear predictive coding (LPC) model. The DCT-encoded data was then reconstructed and tested for intelligibility. It was found that the two-dimensional DCT method was significantly more intelligible and more natural-sounding than the LPC technique.