| 摘要 |
A television receiver can be used both to generate a picture and sound from a broadcast video signal or to generate just a picture from a locally produced video signal, such as one provided by a video camera. A muting apparatus suppresses the sound generated from the broadcast video signal while the television receiver is used as a monitor for the locally produced video signal. The muting apparatus comprises a level shifter that raises the level of the broadcast video signal. A switching means provides to the picture tube of the television receiver either the broadcast video signal or, if the video camera is plugged into the receiver, the locally produced video signal. The level of the signal supplied to the picture tube is sensed; if it is below the predetermined level a muting means connects the audio component of the broadcast video signal to ground to prevent sound from being generated while the receiver is used as a monitor. |
