| 摘要 |
PURPOSE:To use a conventional signal level for an external microphone by setting a signal level sent from a built-in microphone to an amplifier different from a signal level of an external microphone so as to utilize the excellence of the S/N ratio of a built-in microphone. CONSTITUTION:When a microphone plug is not inserted to an external microphone jack 16, a 2nd switch 15 gives a signal from a built-in microphone 18 to an amplifier 11 and a 1st switch 14 connects a 1st negative feedback circuit 12 to the amplifier 11. Thus, the gain of the amplifier is low and the signal level sent from the built-in microphone 18 is high, then the S/N depends on the noise level of the built-in microphone 18. When a microphone plug is plugged into the external microphone jack, the 2nd switch 15 gives a signal from the external microphone plugged into the microphone jack to the amplifier 11 and the 1st switch 14 connects the 2nd negative feedback circuit 18 to the amplifier 11 and the gain of the amplifier is unchanged from the conventional system. Thus, the excellence of the S/N of the built-in microphone is utilized and the compatibility of the external microphone is maintained. |
