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Line Echo Canceller
The line echo canceller (LEC) in optimized to provide the maximum attainable transparent voice quality for de-echoing of a PSTN or POTS connection in VoIP / LAN systems with internal delays, or on a codec end of a telecom switch.
LEC exhibits very fast, typically 'the first phoneme' convergence due to the use of a regularized derivative of theoretically optimal Recursive Least Square (RLS) / Calman algorithm.
LEC has wide dynamic range (down to -65 dBm); is capable of converging on background noise even before parties start talking.
LEC uses very sensitive double-talk detector to ensure that low-level signals like sounds of breathing and distinctive background noise are not clipped out in normal double-talk conditions.
LEC uses Wiener-type post filtering to remove non-linear remnants of the echo (residual echo), to enhance full-duplex transparency during low-level double talk. That results in perceived double talk range beyond 40 dB on m/A-law codecs.
LEC recognizes tonal (any frequencies) or otherwise singular
or narrow-band signals with poor eigen-value spectrum, to prevent its mis-convergence.
LEC has fast detection of echo path change.
LEC ensures smooth transition between matching comfort noise and real background noise, to result in perceptually insignificant noise contrast.
LEC is designed as a system component rather than a stand-alone algorithm; provides statistics and is capable of non-intrusive monitoring.
The archive with ANSI C, 'C54xx, 'C55xx Source code is available from download page.
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