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Line Echo Canceller Software (G.165 Software)
Floreat’s Line Echo Canceller Software implements the ITU-T G.165 recommendation. Line Echo cancellers are voice-operated devices placed in the four-wire portion of the circuit which reduce the echo by subtracting the echo estimate from the circuit echo. In this usage, the echo cancellers are assumed to be half echo cancellers; i.e., those in which cancellation takes place only in the circuits send path, due to signals present in the receive path.
Electrical echo cancellers are widely used in full duplex modems, in which the transmit signal and the receive signal are sent over the same pair of telephone wires. A hybrid unit is required to convert four-wire communication into two-wire communications and vice-versa. These hybrid units are located in the telephone sets, as well as at various telephone exchanges. Because of the non-stationary nature of various communication links, the hybrids cannot be perfectly tuned using hardware adjustments. Thus, a part of the received signal is reflected as echo, known as the electrical echo. Electrical echo cancellers are designed to remove this echo from the transmitted signal and are categorized into near-end echo cancellers and far-end echo cancellers.
The Floreat G.165 Line Echo Canceller software (LEC Software) is modular, re-locatable and re-entrant to support multi-channel capability and can operate within a multi-tasking environment or as a single task.
It supports user callable functions and can be integrated with Floreat’s other fax, telephony, speech compression, VoIP, FoIP, DSVD, imaging and video software for various applications. Floreat G.165 LEC software is supported on various DSPs and processors as well as offered in ANSI C.
Features:
Conforms to ITU-T G.165 requirements
Supports tail length up to 64 ms
Supports user callable functions
Utilizes Normalized LMS (NLMS)
Fast convergence
Low echo return level during single talk
Double talk detector avoids divergence during double talk
Tone detector and hold release logic
Non linear processor
CNG modules can be optionally added for enhanced performance
Easily portable, re-entrant and re-locatable code
C callable APIs
Line Echo Canceller Software (G.165 Software) printable pdf version 
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