Low - Delay Wideband Speech Coding Using a New Frequency Domain Approach

In this paper a new frequency domain approach suitable for low-delay wideband speech coding is proposed. Working in the context of residual speech coders, the proposed technique performs a decomposihon of the D I T of the target vector, (the input speech after the subtraction of the zero input response signal), as the product of the DFT of the impulse response of the LPC synthesis filter and a so called modified residual signal. At the receiver the DFT of the target vector is reconstructed by multiplying the quantized modified residual signal by the D R of the impulse response of the synthesis filter, the inverse DFT calculated and the resulting time domain quantized target vector filtered by the inverse synthesis filter in order to get the excitation to the LPC synthesis filter. Magnitude-phase and real-part-imaginary-part encoding of the modified residual signal has been studied and several quantizations schemes used. Specifically scalar quantization and trellis coded quantization have been used in the development of 32 kbps coders with a very high quality of the synthesized speech. A 24 kbps coder has been developed too by using vector quantization and trellis coded quantization in a magnitude-phase representation of the modified residual.