| 摘要 |
PURPOSE:To give the higher priority to an external signal than an acoustic signal for reproduction by mixing these two signals after changing automatically the sound level ratio between both signals by a signal supplied from outside. CONSTITUTION:For a detecting circuit 3 and a mixing circuit 4, a transistor (TR) 7 amplifies the current of an external signal given from a preamplifier 1 and starts charging by a resistance 8 and a capacitor 9 with the output of amplification. A TR11 is switched by the potential of the capacitor 9, and accordingly TR12 and TR13 are switched. As a result, the sound volume level ratio is changed between sound volume amplifiers 1 and 2. When the signal of the amplifier 1 does not exist any more, the discharge is gradually started by a resistance 10 and the capacitor 9. Thus TRs 11-13 are reset to their previous states respectively and reproduce the signal sent from the amplifier 2 at the preceding sound volume level. Thus the level of the acoustic signal which is under reproduction is lowered by an external signal. Then the higher priority of reproduction is given to the external signal than the acoustic signal.
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