A DFT-based residual-excited linear predictive coder (RELP) for 4.8 and 9.6kb/s
H. Katterfeldt · 2005
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 reiφ. 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.