| 摘要 |
PURPOSE:To prevent generation of noise when a level around a threshold value is inputted consecutively like a voiceless sound by providing two threshold values discriminating the presence or absence of voice to the gain characteristic of an automatic gain control circuit so as to provide a hysteresis characteristic. CONSTITUTION:When an output of a level detection circuit 10 is larger than a threshold value from a threshold value selecting circuit 30, a threshold comparator circuit 20 outputs a low threshold value selecting signal, a hold circuit 40 holds this signal for one frame's share and its output is inputted to the selection circuit 30. The circuit 30 selects a low threshold value by using this signal. When the relation is reverse, a high threshold value is selected similarly. The threshold value selected by the circuit 30 is compared with an output of a level detection circuit after one frame by the circuit 20. Thus, the switching of the threshold value is selected in the level of the input signal so as to give a hysteresis characteristic to a threshold value of the gain characteristic. A gain decision circuit 70 selects the gain characteristic of the threshold value, outputs a coefficient deciding the characteristic, and a gain multiplier circuit 80 provides a gain characteristic with the hysteresis characteristic in the input signal level by using the input signal and said coefficient and outputs the result. |
