| 摘要 |
PURPOSE:To eliminate the discordant noise of the acoustic image expanding circuit to prevent uncomfortable impression of the audience, by adding noise eliminating rotation to the acoustic image expanding circuit. CONSTITUTION:The difference signal of L-R input is delayed by BBD 11 and is mixed into left and right sound signals as indirect sound at a stereo broadcast receiving time. Therefore, attendance impression and expanding impression can be obtained, and then, uncomfortable impression is given due to noise for idle channel. For the purpose of preventing this uncomfortable impression, video signal detecting circuit 20 is provided which outputs a low-level voltage for synchronizing signal ''presence'' of the television signal and outputs a high-level voltage for synchronizing signal ''absence''. This circuit is connected to video detecting circuit 19, and the output of video signal detecting circuit 20 is connected to the base of transistor 21. The collector side of transistor 21 is connected to acoustic image expanding switch 12 which issues indirect sound for high-level input and issues the command to cut off indirect sound for low-level input under the grounded state, and a noise eliminating circuit is provided which is connected to DC power source VCC through the collector side and resistance R. |
