Efficient encoding of speech LSP parameters using the discrete cosine transformation

The intraframe and interframe correlation properties are used to develop two efficient encoding algorithms for speech line spectrum pair (LSP) parameters. The first algorithm (2-D DCT), which requires relatively large coding delays, is based on two-dimensional (time and frequency) discrete cosine transform coding techniques; the second algorithm (DCT-DPCM), which does not need any coding delay, uses one-dimensional discrete cosine transform in the frequency domain and DPCM (differential pulse-code modulation) in the time domain. The performances of these systems for different bit rates and delays are studied, and appropriate comparisons are made. It is shown that an average spectral distortion of approximately 1 dB² can be achieved with 21 and 25 bits/frame using the 2-D DCT and DCT-DPCM schemes, respectively. This is a noticeable improvement over the previously reported bit rates of 32 bits/frame and above.