A DFT-based residual-excited linear predictive coder (RELP) for 4.8 and 9.6kb/s

The proposed RELP system is based on a DFT (discrete Fourier transform) of the linear prediction residual. The base-band Fourier coefficients, derived from frequencies 0 to 800 Hz, are transmitted to the receiver. For encoding, the Fourier coefficients are converted to polar representation re^iφ. The quantization accuracy of both magnitude and phase angle is controlled by an adaptive-bit assignment algorithm. At the receiver, the non-transmitted Fourier coefficients are replaced by base-band coefficients which have been frequency-shifted pitch-synchronously. In the 4.8 kb/s version, the spectral translation algorithm is controlled only by the transmitted pitch frequency. In the 9.6 kb/s version, however, additional information for reconstruction of the harmonic structure in the high-frequency region is computed at the transmitter. Audio tapes of both versions are presented.