| 摘要 |
PURPOSE:To prevent an in-band noise for measuring a side tone coupling loss quantity, from brought to loudspeaking in the own conference room by obstructing the passing of a signal of a receiving channel, when a level ratio of a frequency component of an in-band noise from a conference telephone system of the other party is a prescribed party. CONSTITUTION:When a measurement of a side tone coupling loss is executed in a conference room of the other party side, an in-band noise for a measurement use is inputted to an A/D converting circuit 6 and a filter circuit 14 through a two-wire/four-wire converting circuit 8 from a conference telephone system of the other party. This noise is an in-band noise containing all spectrums of a transmission frequency band, therefore, signal levels of a low frequency and a high frequency from the filter circuit 14 become almost the same level. Accordingly, in a controlling circuit 7, levels of these two frequencies are compared, and in case when both the frequencies have become almost the same level, a receiving channel switch 15 is detached, and this in-band noise is prevented from being outputted from a loudspeaker 10. |
