High Performance Echo Cancellation for Asterisk (HPEC)
For Asterisk users that connect to the PSTN, the most common type of echo is hybrid echo - the echo introduced by the impedance mismatch between 2-wire and 4-wire telephone circuits. The echo manifests as a distorted and delayed reflection of the users voice while in conversation with an external party through the PSTN. HPEC Toll-Quality echo cancellation software is designed to operate under 32-bit and 64-bit Linux on x86-32 and x86-64 compatible processors, and provides echo cancellation for configurable tail lengths of 16ms (128 taps), 32ms (256 taps), 64ms (512 taps), and 128ms (1024 taps).
HPEC software canceller requires only a moderate amount of CPU time / MIPS in order to effectively regulate echo. Digium recommends that users requiring 8 channels at 1024 taps run a PC comparible to a 3.0 GHz Pentium 4, while users only requiring 4 channels at 1024 taps may run a 2.5 GHz Pentium Celeron. The CPU requirements are such that it is impractical to operate this echo canceller at 1024 taps for a full T1 or E1 of channels.
For hardware echo cancellation, Digium provides DSP-based echo cancellation modules for all T1/E1/J1, analog and BRI/Hybrid card models.