For Asterisk users who 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. Asterisk itself offers a range of software-based open source echo cancellation routines that are moderately effective in eliminating the hybrid mismatch echo that most Asterisk users experience.

However, there are cases in which these algorithms are not effective. To combat this, Digium introduced DSP-based echo cancellation modules for our multi-port T1/E1/J1 cards and our 24-port analog card.

Now, Digium is pleased to make available the VPMADT032 echo cancellation module. This module, which offers 128ms (1024 taps) of echo cancellation across all of its channels, improves upon the older VPM100M echo cancellation module, that only offered 32ms of echo cancellation. The VPMADT032 provides the same toll-quality G.168 compliant echo cancellation found in Digium's HPEC software-based commercial echo canceller. The VPMADT032 is immune from any system CPU spikes that might otherwise affect a software-based solution.