| 摘要 |
PURPOSE:To prevent the masking of an ambient noise by a speaker tone by performing volume control by subtracting the output of a composite tone of the speaker tone and ambient noise from the output of a volume controller. CONSTITUTION:A direct-current output obtained by converting from a composite tone of a speaker tone and ambient noise is subtracted from that obtained by converting from the output-side tone signal of volume controller 3 to reduce a speaker tone component nearly to zero and the volume of the sound signal is controlled by this subtraction output. Then, level comparator 22 makes a level comparison between the direct-current output of the sound signal of controller 3 and that of the composite tone and when the former is greater, comparator 22 memorizes and holds the substraction output and also resets a memory holding function repeatedly at constant cycle and for certain time, thereby controlling the volume of the sound signal by the subtraction output. Consequently, the variation of volume controller 3 can be made gentle and a masking phenomenon can also be relieved. |
