| 摘要 |
In an automatic telephone answering system which records and reproduces an outgoing message to be sent to a calling party and an incoming message from the calling party on a recording medium, such as magnetic tape, a single-tone test signal from a touch tone signal generator is recorded on the tape as a cue signal to indicate a position of one of the incoming and outgoing messages. The single-tone signal is also used for a variety of signals in the operation of the automatic telephone answering system, such as a beep tone, an instruction signal and an alarm signal. The reproduced cue signal which is within an audio band is discriminated from an audio signal representing the outgoing or incoming message by a phase-locked loop having a narrow capture range and a loop filter with a prolonged time constant.
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