| 摘要 |
PURPOSE:To make a volume adjustment automatically by an increase and decrease in noise level and also to prevent signal distortion, by providing an upper limit to gain limiting operation, depending upon a noise level at the circumference of a sound field, according to the volume adjustment through manual operation. CONSTITUTION:To control the gain to input signal VIN by control signal CC1 generated by noise detecting circuit 4 detecting a noise at the sound-field circumference and gain limiting signal VC2 from volume adjusting circuit 2, either differential transistor Q1 or Q2, i.e. transistor Q1 is applied with VC1 in variable gain circuit 1, and the other transistor Q2 with VC2 while input signal VIN is supplied to the common emitter. Therefore, as noise detection signal VC1 increased, the conductivity of transistor Q1 is increased to increase the gain. On the other hand, as gain limiting voltage VC2 rises, the conductivity of transistor Q2 is increased to cancel the gain increase by noise detection voltage VC1. |
