| 摘要 |
PURPOSE:To prevent an excessive sound volume from being outputted even in case of erroneous operation by causing a sound level detection part to belong to a gain control circuit. CONSTITUTION:Gain increasing signal Su or reducing signal Sd is formed according to operation switches 21U and 21D or signals from mike 22, and during this time, contents of pulse counter 26 from a pulse generator are subjected to addition and subtraction. The contents are converted to a DC voltage by D/A converter 28 to change the gain of amplifier 12. When a sound level below a prescribed value is detected in this circuit, the output of detector circuit 29 becomes 0, and gain-increased pulses from AND 24U are cut by AND 27 to subject contents of counter 26 to no addition, thereby preventing the increment of the sound volume. |
