Echo Cancellation
Hybrid Echo Cancellers
One of the primary challenges faced by service providers in delivering quality voice communications is the elimination of the hybrid echo that is present on almost all calls terminating or originating on a landline (PSTN) connection. The echo traditionally results from signal reflection at the hybrid, where the two wires of the local analog network meet the four wires of the digital network. The hybrid is not completely efficient in carrying the electrical energy, so a certain amount of the electrical energy (or voice signal) is reflected back. If there is delay across the network, the reflected signal is perceived as echo.
Almost all networks experience echo since at least some of the calls originate or end in a PSTN network. In addition, as networks become more complex with the convergence of wireline, wireless, and VoIP, increased delays make the echo more noticeable and intrusive.
Service providers deploy echo cancellation technology to address this problem. The echo canceller (EC) samples the voice signal and estimates and removes the echo, leaving the original speech. A digital signal processor (DSP) algorithm is used to estimate, invert, and cancel the main (linear) echo components, typically followed by a process referred to as non-linear processing (NLP), where any remaining residual echo components are eliminated.
Industry-Leading Solutions
Ditech Networks' hybrid echo cancellation (HEC) products address the effects of hybrid echo with an industry-leading tail delay capability of up to 192 ms, ensuring consistently clear, echo-free calls, even in the face of network migration from TDM to VoIP. Ditech provides specific echo cancellation solutions for the following network situations:
| Echo Cancellation | Echo Cancellation with VQA | |
| Wireline | Yes | Contact Us |
| Bidirectional Wireline | Yes | - |
| International Gateway | Yes | Contact Us |
| Satellite | Yes | Contact Us |
| Wireless | Yes | Yes |
| Conferencing Services | - | Yes |
| VoIP-PSTN Gateway | Yes | Yes |
| VoIP Network | Yes | Yes |
With a fast, stable convergence of less than 50 ms, Ditech’s solutions cancel echoes with an echo return loss of 0 dB (the worst possible case, where the reflected energy is equal in strength to the original signal), ensuring complete hybrid echo cancellation in all situations.