Double talk detector for echo cancellers

An echo cancellation circuit having a reception line for providing a distant party signal received from a distant party;

• a transmit line having a near party signal from a near party and an echo signal applied thereto for providing a composite signal;
• a filter for receiving said distant party signal at a filter input and producing a signal which estimates said echo signal, said estimated signal being produced after an initial adaptive period;
• subtraction means for subtracting said estimated signal from said composite signal to produce an intermediate signal along said transmission line;
• signal suppression means for receiving said intermediate signal and for producing a transmitted signal;
• a first detector receiving said distant party signal and said composite signal and providing a first output signal when a first predetermined quantitative relationship exists between said distant party signal and said composite signal;
• a second detector receiving said distant party signal and said intermediate signal and providing a second output signal when a second predetermined quantitative relationship exists between said distant party signal and said intermediate signal;
• a third detector receiving said composite signal and said intermediate signal and providing a third output signal when a third predetermined quantitative relationship exists between said composite signal and said intermediate signal;
• and logic means receiving output signals from each of said first, second and third detectors, wherein said logic means selectively enables and disables said filter means and suppression means under the control of said first, second and third detector output signals.

In an echo cancellation circuit having a receive line for receiving a distant party signal received from a distant party, a transmit line having a near party signal from a near party and an echo signal applied thereto for providing a composite signal, a filter having a filter input for receiving said distant party signal and having a selectively enabled and disabled adaptive process for producing a signal which estimates said echo signal, said estimated signal being produced after an initial adaptive period, subtraction means for subtracting said estimated signal from said composite signal to produce an intermediate signal along said transmission line, signal suppression means having selectively enabled and disabled states for receiving said intermediate signal and for producing a transmitted signal, the improvement comprising:

• first means for generating an output signal indicating whether or not said initial adaptive period is ended;
• first double talk detection means for generating a first control output signal when a first quantitative relationship exists between said distant and near party signals;
• second double talk detection means for generating a second control output signal when a second quantitative relationship exists between said intermediate and distant party signals;
• and
• control means responsive to said first means output signal and to said first and second control output signals for controlling the enablement and disablement of said signal suppression means and said filter means in accordance with said first control signal during said initial adaptive period of said filter means and for controlling the enablement and disablement of said signal suppression means and said filter means in accordance with said second control output signal after said initial adaptive period.

In an echo cancellation circuit having a reception line for providing a distant party signal received from a distant party;

• a transmit line having a near party signal from a near party and an echo signal applied thereto for providing a composite signal;
• a filter for receiving said distant party signal at a filter input and producing a signal which estimates said echo signal, said estimated signal being produced after an initial adaptive period;
• subtraction means for subtracting said estimated signal from said composite signal to produce an intermediate signal along said transmission line;
• signal suppression means for receiving said intermediate signal and for producing a transmitted signal;
• a first detector (DTD1) for generating a first detection signal in response to the existence of a first quantitative relationship between said distant and near party signals;
• and first means for enabling and disabling at least one of said filter and signal suppression means in response to said first detection signal;
• the improvement comprising:
• means for determining the end of said initial adaptive period;
• and
• a second detector (DTD2) for generating a second detection signal in response to the existence of a second quantitative relationship between said intermediate signal and said distant party signal, said first means disabling at least one of said filter and said signal suppression means in response to said second detection signal only after the end of said initial adaptive period is determined.