| 摘要 |
PURPOSE:To attach a characteristic with superior quality on a fast modem signal without deteriorating reproducing sound quality, by distinguishing strictly an input signal whether it is a sound signal, or a modem signal, and using a quantizer having the optimum size and an adaptive speed respectively for a sound signal input and a modem signal input. CONSTITUTION:The difference between the outputs of a short range integrator 211, and a long range integrator 212, is found at a comparator 213, and it is recognized as the sound signal when the difference is larger than a threshold level regulated in advance, and also, at the comparator 213, the input signal is recognized as the sound signal when the value of a step size is smaller than a certain threshold level, and a control parameter (alpha) is increased at a parameter generating part 214 respectively in both cases. A bracketing parameter BP having the average of the control parameters (alpha) for a considerable long time is generated at a smoothing filter 215. A switching discriminating part 216 compares a threshold level BPS that brackets the sound signal from the modem signal, and the BP, and generates a parameter CF that discriminates the sound signal from the modem signal. A quantization step size adaptive control part 208 changes the size of a step size on the basis of the discriminating flag CF.
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