ENHANCED CONVERSION OF WIDEBAND SIGNALS TO NARROWBAND SIGNALS

摘要

Wideband speech signal must be converted to narrowband speech signals if the transmission medium or the destination termianl is constructed with narrowband constraints. A typical wideband-to-narrowband conversion method is the elimination of frequencies above 3400 Hz using a low pass filter and a down sampler. Howerver, this method producesa muffled speech sound since the resulting narrowband signal has a flat frequency response. Methods and apparatus are presented herein to enhance the acoustinc quality of a wideband-to-narrowband converted signal. A bandwidth switching filter (68) is used to emphasize a mid-range frequency portion of the wideband signal to that the resulting narrowband signal has a non-falt frequency spectrum.