| 摘要 |
PURPOSE:To perform weighting operation even when an electronic volume control is usd and allow a low-frequency sound to be heard sufficiently, specially, when the sound volume is small by providing a variable gain circuit whose gain is controlled according to a control voltage and an impedance element which is connected between the input and output terminals of the variable gain circuit and varies in impedance with frequency. CONSTITUTION:An equation holds for the input Vi and output V1 of an initial- stage electronic volume control 4. Then, an equation II holds for a current I which flows through a resistance R and the impedance element Z. Further, an equation III holds for the input V2 of a trailing-stage electronic volume control 5. Therefore, the output V0 of the electronic volume control 5 is as shown by an equation IV. The output V0 when A=1 in the equation IV, i.e. at the time of the maximum gain is as shown by an equation V and the output V0 when A=0, i.e. at the time of a minimum gain is as shown by VI. When the gain A is between 0 and 1, the output V0 shows frequency characteristics depending upon the impedance of the impedance element Z. For the purpose, the impedance element Z uses an element shown in figures (a) and (b) to obtain such a characteristic that a resonance frequency f0 rises at the time of a low gain. |
