| 摘要 |
PURPOSE:To improve the tone margin at low and high frequencies by using a flat circuit provided at the input side of an echo canceller so as to make the spectrum of an input signal flat and smoothing the difference between the signal at the output terminal and the input signal. CONSTITUTION:When an echo comes to an outgoing channel W in a 2/4-wire converter 2B, the echo signal is given to a half wave rectifier circuit 5B, where the frequency spectrum is made flat and the result is inputted to a transmission input terminal Sin of the echo canceller 7B. On the other hand, since a signal smoothing the spectrum is fed similarly to a reception input terminal Rin of the echo canceller 7B, the echo canceller 7B applies echo elimination over the entire frequency of the echo signal as shown in an Sout signal. The similar operation is applied as to the signal inputted from a 2-wire input terminal 1B.
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