| 摘要 |
PURPOSE: To detect the noise level in car room and to amplify the low tone band of regenerative signal and signal of a prescribed level or below in accordance with the noise level. CONSTITUTION: Traveling noise is detected by a microphone 11 placed in the car room, and signal level A of a detection band is obtained by a low-pass filter 13 and a rectifier means 14, and also for audio regenerative signal, the signal level B of the detection band is obtained by the low-pass filter 7 and the rectifier means 15 from an output of a D/A converter 8. By gain controlling to satisfy A≈B at no noise time, the real noise level is obtained by performing processing of A-B by an adder 17 when a noise occurs after adjustment, and the result is classified by level by a noise level detection means 18, and a signal processing means 4 is controlled according to the noise level, and the low tone band is amplified, and the signal of the prescribed level or below is amplified.
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