15-02-2017, 02:13 PM
VOCAL offers a range of echo cancellation solutions, including acoustic echo cancellers (AEC) and line / network echo cancellers (LEC / NEC). We have extensive experience in developing, integrating and configuring echo cancellation solutions on a wide variety of products. Contact us to discuss your request for cancellation of echo.Echo Cancellation is the reduction of the reflected copies of a wave of direct path in a signal. In telephony, the source of these reflections may be generated electrically due to a mismatch of impedance in the transmission path or as a result of an acoustic and / or mechanical coupling between a loudspeaker and a microphone, usually because they are in the same enclosure physical. An acoustic echo canceller (AEC) is required for acoustic / mechanical coupling; While, a line echo canceller (LEC) is used to solve the impedance mismatch.
Adaptive Filters
An adaptive filter is used in echo cancellation of voice to accommodate the variable nature in the time of the echo path. The filter learns the path when the far end speaker is talking and the near end speaker quietly and adjusts its coefficients (transfer function) according to the criterion of algorithm optimisation.
Echo Tail Length
The echo tail length is considered the length of the echo path pulse response. The required length of the queue depends on the application. For line echoes, the pulse is generally in the range of 8 to 32 ms, whereas the acoustic impulse responses may be on the order of 100 ms.
Dual talk detection
For an adaptive filter to learn the echo path must have an undisturbed reference signal to adapt to. Unfortunately, in full-duplex communications, this scenario can not be guaranteed, as the nearby speaker may want to interrupt the far-end speaker. In other words, the near-end and far-end speakers will be speaking simultaneously (double-talk), resulting in disturbances in the reference signal. These disturbances will result in divergent behaviour of the adaptive filter and double-talk detection is required to retard filter adaptation and avoid divergence.
Nonlinear Processing
Nonlinear processing is the removal of the residual echo left by the adaptive filter. Residual echoes are the non-modelled components of the echo path. Most adaptive filters are linear and can only cancel the linear parts of the echo path. Thus, the non-linear portions can not be eliminated through the adaptive filter and a residual echo suppressor follows the filter to handle remaining non-linear echo parts.
Adaptive Filters
An adaptive filter is used in echo cancellation of voice to accommodate the variable nature in the time of the echo path. The filter learns the path when the far end speaker is talking and the near end speaker quietly and adjusts its coefficients (transfer function) according to the criterion of algorithm optimisation.
Echo Tail Length
The echo tail length is considered the length of the echo path pulse response. The required length of the queue depends on the application. For line echoes, the pulse is generally in the range of 8 to 32 ms, whereas the acoustic impulse responses may be on the order of 100 ms.
Dual talk detection
For an adaptive filter to learn the echo path must have an undisturbed reference signal to adapt to. Unfortunately, in full-duplex communications, this scenario can not be guaranteed, as the nearby speaker may want to interrupt the far-end speaker. In other words, the near-end and far-end speakers will be speaking simultaneously (double-talk), resulting in disturbances in the reference signal. These disturbances will result in divergent behaviour of the adaptive filter and double-talk detection is required to retard filter adaptation and avoid divergence.
Nonlinear Processing
Nonlinear processing is the removal of the residual echo left by the adaptive filter. Residual echoes are the non-modelled components of the echo path. Most adaptive filters are linear and can only cancel the linear parts of the echo path. Thus, the non-linear portions can not be eliminated through the adaptive filter and a residual echo suppressor follows the filter to handle remaining non-linear echo parts.