Telephone terminal, telephone system using telephone terminal and control method of telephone terminal

A telephone system equipped with a main device for performing a line exchange and a plurality of telephone terminals which are connected to the main device via a cable line, transmits a voice signal to the main device and receives it transmitted from the main device to acoustically reproduce it, wherein each of the telephone terminals comprises:

• a receiving detector which detects a signal level of a receiving voice signal incoming from the main device;
• a transmitting detector which detects a signal level of a transmitting voice signal to transmit it to the main device;
• an adjustment device configured to adjust the transmitting voice signal;
• and
• a controller which obtains a control value capable of switching a communication state from a receiving state to a transmitting state to make an acoustic echo to be added to the transmitting voice signal be minimum based on each a detection result of the receiving detector and a detection result of the transmitting detector, and controls the adjustment device based on the control value.

A control method of a telephone terminal for use in a telephone system equipped with a main device for performing a line exchange and a plurality of telephone terminals which are connected to the main device via a cable line, transmits a voice signal to the main device and receives it transmitted from the main device to acoustically reproduce it, comprising:

• detecting a signal level of a receiving voice signal incoming from the main device;
• detecting a signal level of a transmitting voice signal to transmit it to the main device;
• obtaining a control value capable of switching a communication state from a receiving state to a transmitting state to make an acoustic echo to be added to the transmitting voice signal be minimum based on each signal level of the receiving voice signal and signal level of the transmitting voice signal;
• and
• adjusting to control the transmitting voice signal based on the control value.