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Browse Prior Art Database

High Attenuation Digital Echo Suppressor

IP.com Disclosure Number: IPCOM000089112D
Original Publication Date: 1977-Sep-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Lenoir, R: AUTHOR

Abstract

Transmission lines are provided with hybrid transformers to perform two-to-four wire conversion in order to achieve separation between the transmit channel and the receive channel. As shown on the figure, this leads to a looped circuit which could generate local echo noise. To avoid this situation, each channel is provided with an echo noise suppressor including a feedback equalizer, the taps of which are adjusted for noise cancellation. However, in a double-speech situation, i.e., both terminals transmitting, the equalization is impossible. Whenever this now occurs, one of the terminals is blocked quite arbitrarily, for instance, the louder speaker cuts out the other one.

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High Attenuation Digital Echo Suppressor

Transmission lines are provided with hybrid transformers to perform two-to- four wire conversion in order to achieve separation between the transmit channel and the receive channel. As shown on the figure, this leads to a looped circuit which could generate local echo noise. To avoid this situation, each channel is provided with an echo noise suppressor including a feedback equalizer, the taps of which are adjusted for noise cancellation. However, in a double-speech situation, i.e., both terminals transmitting, the equalization is impossible. Whenever this now occurs, one of the terminals is blocked quite arbitrarily, for instance, the louder speaker cuts out the other one.

A system is here proposed to avoid the use of this arbitrary solution. As shown in the figure, the terminal on side A is connected to a hybrid transformer H(A) connected on one side to a transmit path through a DAC F/1/(A). A balanced impedance A(A) is also provided.

The terminal on side B is connected to a similar network comprising a hybrid transformer H(B) with balanced impedance Z(B), an ADC amplifier F(B) and an ADC amplifier F/1/(B).

Suppose that the terminal on side A is talking. The information normally goes through H(A), F(A), F/1/(B) and H(B) to the terminal on side B. However, one could not avoid a part of the signal being fed back through H(B), F(B) and F/1/(A) to terminal A. This echo noise is cancelled by using an equalizer EqB and a subtr...