| 摘要 |
PURPOSE:To stop the ringing tones without deteriorating the sound quality by providing a step changing device for call signal at the transmission or reception side of a bidirectional and simultaneous communication equipment using a microphone and a speaker. CONSTITUTION:The signal sent from a microphone 10 is amplified 11 and delivered to a talking circuit 17 via a buffer amplifier 12. The signal deteriorated by the circuit 17 is equalized by an equalizer 13. Then the equalized signal is amplified by a power amplifier 14 for drive of a speaker 15. A ringing tone stopping device 16 is provided at a part of the reception side of a bidirectional and simultaneous communication device. The device 16 increases or decreases the step of the signal supplied from the device 16 by such a degree, e.g., half octave or so that causes no change of the sound quality. Thus the phase of an output signal is completely different from that of an input signal. Therefore no acoustic connection is produced between the microphone 10 and the speaker 15. This eliminates a positive feedback loop and prevents the generation of ringing tones.
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