Method and device for suppressing echo in a hands free device such as a telephone

A device for echo suppression in a handsfree apparatus, comprising:

• an adaptive filter;
• a first adjustable amplifier associated with a receiving path of the handsfree apparatus,
• a second adjustable amplifier associated with a transmitting path of the handsfree apparatus;
• and
• a control unit including a first short-term power estimator, at least one further short-term power estimator, a control logic unit, a first nonlinear shaping filter and a second nonlinear shaping filter, the control unit outputting a first control signal and a second control signal, the first short-term power estimator outputting a signal for measuring a power of a far-end subscriber signal, each output of the at least one further short-term power estimator at least one of forming individually and forming in combination a signal for measuring a power of a near-end subscriber signal,
• wherein the control logic unit has inputs including a first control variable U1, a second control variable U2, a first predetermined threshold value S0 and a second predetermined threshold value S1, the control logic unit having outputs including a first output signal Vτ, a second output signal V1 and a third output signal V2,
• wherein the first nonlinear shaping filter is associated with the transmitting path, the first nonlinear shaping filter being supplied with the second output signal V1, the first nonlinear shaping filter outputting the second control signal,
• wherein the second nonlinear shaping filter is associated with the receiving path, the second nonlinear shaping filter being supplied with the third output signal V2, the second nonlinear shaping filter outputting the first control signal,
• wherein the first control variable U1 is a sum of the signal for measuring the power of the near-end subscriber signal and the signal for measuring the power of the far-end subscriber signal,
• wherein the second control variable U2 is a quotient of the signal for measuring the power of the near-end subscriber signal and the signal for measuring the power of the far-end subscriber signal,
• wherein the control logic unit processes the first control variable U1 and the second control variable U2 to form the first output signal Vτ, the second output signal V1 and the third output signal V2 according to rules below where the second predetermined threshold value S1, a first factor α and a second factor β are each less than one:
• a) if U1<S0 then Vτ=0, V1=1 and V2=β,
• b) if U1>S0 and U2<S1 then Vτ=0, V1=α and V2=1,
• c) if U1>S0 and U2>1/S1 then Vτ=1, V1=1 and V2=β, and
• d) if U1>S0 and 1/S1>U2>S1 then Vτ=1, V1=1 and V2=1,
• wherein the first control signal controls an amplification of the first adjustable amplifier in proportion to a magnitude of the first control signal,
• wherein the second control signal controls an amplification of the second adjustable amplifier in proportion to a magnitude of the second control signal, and
• wherein the first output signal Vτ sets at least one of a first time constant and a second time constant of the first nonlinear shaping filter as a function of at least a level of the first output signal Vτ.