| 摘要 |
PURPOSE:To keep an input level to a volume control circuit in constant invariably, by changing the factor of a multiplier which multiplies by the factor on an audio signal, corresponding to a ratio between the output level, and the targeted level of the multiplier. CONSTITUTION:In a volume control device using a digital signal processor DSP, the audio signal from a terminal IN is inputted to a multiplier KA. The output INP, from which a DC component and high frequency noise are eliminated, is smoothed at an LPF1 through a full-wave rectifying absolute value circuit ABS, and the level LEV of it is inputted to a comparator CMP. The CMP compares the LEV with a targeted level Vc, and inputs a multiplier KB which corrects a ratio component COM to a control factor. The output control factor of the KB is inputted to an LPF2 which varies response speed, and the output changes a factor value multiplied on an input signal by the multiplier KA, through a limiter LIM, and a regulator LEG, corresponding to the COM. Therefore, the level INP inputted to a volume control circuit KV can be kept in constant even when the level of the input IN changes.
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