Device and method for suppressing echo in telephones

1. A telephone echo reduction devices, having:

an echo reduction unit ( 4 ), disposed between an input channel ( 1 ) for receiving an input audio signal (A 1 ) coming from a remote telephone, and an output channel ( 5 ) for outputting an output audio signal (A 2 ), and providing for the variable suppression of any echo signal contained in the output audio signal (A 2 ) according to an echo suppression factor (s) at a control input,

a speech activity detection unit ( 7 ) for detecting any speech signal in the input audio signal (A 1 ), wherein, said echo suppression factor (s) is set maximum if a speech signal is detected, and,

a control unit ( 6 ) connected to an input control of the echo reduction unit ( 4 ), and when the speech activity detection unit ( 7 ) indicates no speech signal is being detected, then providing for the echo suppression factor (s) to be gradually and smoothly exponentially decayed from maximum to minimum over a time profile;

wherein, any reverberation echoes that would otherwise occur are reduced.

2. The device of claim 1 , wherein, the control unit ( 6 ) provides for the echo suppression factor (s) to be exponentially decayed in accordance with the function

s[k]=α·s[k− 1]+(1−α)· s low ,

wherein s[k] is the echo suppression value at time k, α is a factor representing the exponential reduction behavior and s low is a minimum echo suppression value.

3. The device of claim 2 , wherein, the control unit ( 6 ) provides for the minimum suppression value s low is in the range 0.1 to 1, and the factor α representing the exponential reduction is in the range of 0.5 to 0.99.

4. The device of claim 1 , wherein, the control unit ( 6 ) provides for time delay of the reduction of the echo suppression factor (s) from 0.1 to 1 second.

5. The device of claim 1 , further comprising:

a second speech activity detection unit ( 427 ) for detection of a speech signal in an echo reduced audio signal (r) fed to the echo reduction unit ( 4 ) and coming from a near end;

wherein, said echo suppression factor (s) is set to a maximum suppression value if the input audio signal has a speech signal and the echo reduced audio signal (r) does not have a speech signal, and;

wherein, the echo suppression factor (s) is set to a medium echo suppression value if the input audio signal (A 1 ) and the echo-reduced audio signal (r) both has a speech signal.

6. The device of claim 1 , further comprising:

an adaptive FIR echo filter ( 40 ) for determining an estimated echo signal (e) in which coefficients of the adaptive FIR echo filter ( 40 ) are initialized at the start of reception of input audio signal (A 1 ) to non-zero.

7. The device of claim 6 , wherein, the control unit ( 6 ) provides for the echo suppression factor (s) to initially be set to a maximum at the start of the reception of the input audio signal (A 1 ) and then reduced if a speech signal remains present in the input audio signal (A 1 ).

8. The device of claim 7 , wherein, the control unit ( 6 ) provides for said reduction in initial echo suppression factor (s) over time to approximate the adaptation duration of the adaptive FIR echo filter ( 40 ).

9. A method for reducing echo in the transmission of audio signals, in particular in uttered speech, having the steps of:

echo suppression for suppressing an echo signal (A 1 ) of an input audio signal (A 1 ) contained in an output audio signal (A 2 ),

detection of a speech signal contained in the input audio signal (A 1 ), and

setting of an echo suppression factor (s) for the suppression of echo,

characterized in that the echo-suppression factor (s) is reduced gradually and continuously exponentially decayed maximum from a echo-suppression value set while a speech signal is present in the input audio signal (A 1 ) to a minimum echo-suppression value if it is detected that the input audio signal (A 1 ) does not contain any speech signal.