| 摘要 |
<p>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.</p> |
