| 摘要 |
PURPOSE:To control the starting level of compression and expansion, by displaying both the level of a sound signal and the level of a DC control signal obtained from the sound signal. CONSTITUTION:The signal obtained by a reproducing head 1 is amplified by a reproducing system containing a noise reducing circuit of a Dolby system. A converting circuit 10 gives the wave detection to a sound signal to obtain a DC signal. A level detecting circuit 11 produces a control signal when the voltage of the DC signal is higher than a certain level. The detecting level can be changed by a resistor 16 and at the same time the level of the control signal is displayed at a display 28. The control signal controls the gain of an amplifier 8. The signal is expanded when it is reproduced, and the expanding ratio is decided by a voltage dividing circuit 23 consisting of a resistance. Both states of expansion and compression are shown through level displays 27 and 28. Thus a change is facilitated for the starting level or the ratio. |
