Communication system

1. A method comprising:

inputting a speech signal into a filter having filter characteristics effective to cause the filter to filter a first portion of the input speech signal to generate a filtered portion of an output signal;

analyzing the filtered portion of the output signal by determining both an energy of a frame of the input speech signal and an energy of a frame of the filtered portion of the output signal;

detecting if ringing is present in the filtered portion of the output signal based on said analysis; and

adjusting the filter characteristics to reduce ringing in a subsequent filtered portion of the output signal if it is determined that ringing is present in the filtered portion by outputting a control signal to the filter effective to cause the filter to filter a subsequent portion of the speech signal to generate the subsequent filtered portion, the control signal configured to dampen an impulse response of the filter.

2. The method as claimed in claim 1 wherein adjusting the filter characteristics allows the output signal to follow the input speech signal.

3. The method as claimed in claim 1 wherein the first portion of the input speech signal is a frame of the input signal.

4. The method as claimed in claim 1 wherein the filtered portion of the output signal is a frame of the output signal.

5. The method as claimed in claim 1 wherein the filter is a notch filter.

6. The method as claimed in claim 5 wherein the filter characteristics are adjusted by increasing a width of the notch filter.

7. The method as claimed in claim 5 wherein the filter characteristics are adjusted by decreasing a depth of the notch filter.

8. The method as claimed in claim 5 wherein the notch filter includes at least one gain element.

9. The method as claimed in claim 8 wherein a width of the notch filter is increased by adjusting a gain coefficient of said at least one gain element.

10. The method as claimed in claim 8 wherein a depth of the notch filter is decreased by adjusting a gain coefficient of said at least one gain element.

11. The method as claimed in claim 1 further comprising:

analyzing the subsequent filtered portion of the output signal;

detecting if ringing is present in the subsequent filtered portion of the output signal based on said analyzing the subsequent filtered portion; and

adjusting the filtering characteristics with an equal and opposite adjustment to the adjustment that was made to reduce ringing if it is determined that ringing is not present.

12. The method as claimed in claim 1 wherein said detecting if ringing is present in the filtered portion of the output signal further comprises:

comparing the energy of the frame of the filtered portion of the output signal to the energy of the frame of the input speech signal; and

determining that ringing is present in the output signal if the energy of the frame of the filtered portion of the output signal is greater than the energy of the frame of the input signal.

13. A device comprising:

a receiver configured to receive a speech signal;

a filter, having filter characteristics, configured to filter a first portion of the speech signal to generate a filtered portion of an output signal;

a controller configured to:

analyze the filtered portion of the output signal by determining both an energy of a frame of the speech signal and an energy of a frame of the filtered portion of the output signal;

detect if ringing is present in the filtered portion of the output signal based on said analysis; and

adjust the filter characteristics to reduce ringing in a subsequent filtered portion of the output signal if it is determined that ringing is present in the filtered portion by outputting a control signal to the filter effective to cause the filter to filter a subsequent portion of the speech signal to generate the subsequent filtered portion, the control signal configured to dampen an impulse response of the filter.

14. The device as claimed in claim 13 , wherein the filter is configured to adjust the filter characteristics to enable the output signal to follow the speech signal.

15. The device as claimed in claim 13 , wherein the first portion of the speech signal is a frame of the signal, and wherein the filtered portion of the output signal is a frame of the output signal.

16. The device as claimed in claim 13 , wherein the filter is a notch filter, and wherein the controller is further configured to adjust the filter characteristics by increasing a width of the notch filter or by decreasing a depth of the notch filter.

17. A communications terminal comprising:

a receiver configured to receive a speech signal;

a filter, having filter characteristics, configured to filter a first portion of the speech signal to generate a filtered portion of an output signal;

a controller configured to:

analyze the filtered portion of the output signal by determining both an energy of a frame of the speech signal and an energy of a frame of the filtered portion of the output signal;

detect if ringing is present in the filtered portion of the output signal based on said analysis; and

adjust the filter characteristics to reduce ringing in a subsequent filtered portion of the output signal if it is determined that ringing is present in the filtered portion by outputting a control signal to the filter effective to cause the filter to filter a subsequent portion of the speech signal to generate the subsequent filtered portion, the control signal configured to dampen an impulse response of the filter.

18. The communications terminal as claimed in claim 17 , wherein the filter is further configured to adjust the filter characteristics to enable the output signal to follow the speech signal.

19. The communications terminal as claimed in claim 17 , wherein the first portion of the input speech signal is a frame of the input signal, and wherein the filtered portion of the output signal is a frame of the output signal.

20. The communications terminal as claimed in claim 17 , wherein the filter is a notch filter, and wherein the controller is further configured to adjust the filter characteristics by increasing a width of the notch filter or by decreasing a depth of the notch filter.