| 摘要 |
PURPOSE:To ensure an effective control of sound volume without giving masking with a low level nor generating an excessive degree of sound volume with a high level even to a music signal having a big level change, by performing an automatic gain control not only to the ambient sound level but to the input signal level. CONSTITUTION:When an ambient noise level detecting circuit 2 supplies the output signal of a sensor 1, the DC voltage is delivered in proportion to the level rise NdB to the reference noise level NodB(A) SPL. While the level of the input signal supplied to a signal input terminal 3 is detected by an input signal level detecting circuit 8. Then the DC voltage proportional to the rise DELTASdB to the reference signal level SodBs is delivered. Thus the compression degree of signal is set constant regardless of the ambient noise level. An adder circuit 11 adds the voltage corresponding to a negative constant DELTAST to the output of a multiplier circuit 10' and supplies them to a gain control circuit 5 via a limiter circuit 13. Thus the sound volume is gradually increased from a low signal level so as to receive no masking to the increase of the ambient noises. |
