ECHO CANCELLATION
Echo cancellers are often required in speech recognition systems due to analog impairments present in the telephone system: These are implemented using simple FIR adaptive filtering techniques: The coefficients of these filters are computed using a least mean-squared error approach (LMS). Such systems are used to allow users to speak during a prompt (barge-in), which is a very important feature of a practical recognition system. A reference implementation of a standard FIR echo canceller is available on-line, along with many educational resources and conference papers on applications to speech recognition.