| 摘要 |
PURPOSE:To superimpose a synchronizing signal almost without expanding a transmission band by A/D converting a sound signal and storing it in a RAM, and providing a time gap in an output signal from the RAM, and transmitting the synchronizing signal as time division multiplexing it in said gap, at a transmitting side. CONSTITUTION:The inputted sound signal is written in a storage circuit 3 through an A/D conversion circuit 2 according to a write-in signal, generated by an address control circuit 9, and next, is read out according to a read-out address. At that time, a privacy processing is performed by changing a read-out delay time and changing a frequency periodically, and at the same time, the time gap is generated in a read-out address. After the synchronizing signal is time division multiplexed in this gap by a synchronizing signal generation circuit 4, it is outputted through a D/A conversion circuit 5 and an LPF 6. Accordingly, the synchronizing signal can be superimposed scarcely expanding the transmission band.
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