To easily compensate a decrease in high-frequency gain of a telephone system signal due to impedance mismatching which is easy to occur when an ASDL telephone device is connected to a line. ASDL電話装置を回線接続する場合に発生し易いインピーダンス不整合による電話系信号の高域利得の低下を簡便に補償すること。 - 特許庁