| 摘要 |
PURPOSE: To attain sound quality and sound volume adjustment in response to a noise level with a small error by correcting a noise estimate vague based on a vehicle speed when noise detection by a microphone is difficult. CONSTITUTION: A voltage corresponding to a vehicle velocity is given to an amplifier 13, an inverted output of the amplifier 13 and an output of a microphone are given to an adder 20, and an output of the adder 20 is fed to a capacitor 22 via a switch 21. Thus, when a noise picked up by the microphone is high even at a prescribed vehicle speed, a DC voltage of the capacitor 22 is increased. When the noise detection by the microphone is difficult, the switch 21 is open and the DC voltage corrected by the noise from the microphone is stored in the capacitor 22 and sound volume and sound quality are adjusted depending on an output of an adder 19 summing the DC voltage and the output of the amplifier 13. |
