Telephone echo canceller
The invention relates to an echo canceling device and method for an arrangement for transmitting audio signals, in particular uttered speech with an echo filter for canceling echo. The echo filter is arranged between an input channel ( 1 ) and an output channel ( 4 ). The input channel ( 1 ) leads a first electrical input signal to a converter ( 2 ) for converting the electrical signal into a first audio signal. The output channel ( 4 ) transmits an electrical signal from a converter ( 3 ) which converts a second audio signal back into an electrical signal. In order to prevent non-linearly distorted echo in such an echo canceling device or method, a high-pass filter ( 8 ) is arranged in the input channel ( 1 ) which high-pass filter ( 8 ) has a cut-off frequency that is beyond the cut-off frequency of the high-pass behavior in the converter ( 2 ). The high-pass filter ( 8 ) is followed by a limiting element ( 9 ) which limits the amplitude of the input signal to the input range of the converter ( 2 ). By this means, non-linear behavior in the converter ( 2 ) is prevented so that non-linearly distorted echo cannot arise at all.
1. A telephone echo canceller, comprising:
an input ( 1 ) to receive an audio input signal from a remote telephone;
an output ( 4 ) to send an audio output signal to said remote telephone;
a high pass filter ( 8 ) for removing signals lower than a cutoff frequency from said audio input signal;
a soft limiter ( 9 ) for limiting the amplitude of signals passed through the high pass filter;
an echo canceller ( 53 ) with a summing point ( 531 ) and a linear adaptive filter ( 532 ), and which inputs signals from the soft limiter ( 9 ) for a convener ( 2 ) and a loudspeaker, and inputs signals from a microphone and inverse converter ( 3 ) for said summing point ( 531 ), and has audio output ( 4 ) taken from said summing point ( 531 ) after subtracting an estimated linear echo provided by said linear adaptive filter ( 532 );
wherein, the combination of the high-pass filter ( 8 ) and soft-limiter ( 9 ) substantially eliminate non-linear components from being included in an acoustic echo ( 7 ) from said loudspeaker to said microphone, and thereby enable a simple linear adaptation and filtering with said linear adaptive filter to substantially remove any adverse effects of acoustic echo ( 7 ) that would otherwise occur.
2. The echo canceller of claim 1 , wherein high-pass filter ( 8 ) has a 3-dB cut-off frequency in the range of 0.1-2 kHz.
3. The echo canceller of claim 1 , wherein high-pass filter ( 8 ) has a 3-dB cut-off frequency in the range of two to ten times that of a 3-dB cut-off frequency of the converter ( 2 ).
4. A method of echo canceling in a telephone, comprising:
removing low frequency ( 8 ) signal components from an audio input signal received by an input channel ( 1 ) from a remote telephone;
soft-limiting ( 9 ) the amplitude of said audio input signal after said removal of said low frequency signal components, such that non-linear acoustic components Will be substantially removed from an echo ( 7 ) between a loudspeaker device ( 2 ) and a microphone device ( 3 ); and
using only linear adaptation and filtering ( 532 ) in an echo canceller ( 53 ) connected to the loudspeaker device ( 2 ) and microphone device ( 3 ) to remove substantially all echoes from an audio output signal at an output ( 4 ) directed to said remote telephone.