The near-end speaker confuses the echo identification process, thus limiting the effectiveness of the echo canceler. In addition, the echo canceler must not clip the beginning of the double-talk session. The double-talk detector works in most cases, but when it fails to detect double talk, some echo is still noticeable. The echo canceler also must identify and remove background noise. Once an echo is identified, the echo canceler subtracts the echo from the returning signal.
Echo cancellation can be highly resource-intensive.
The amount of processing power necessary to compare and filter out echo may be so high as to be detrimental to the vendor's overall solution. Since processing power is a finite resource, as more resources are diverted to echo cancellation, fewer resources are available for processing additional voice channels. Mapletree's engineers have developed an echo-cancellation technique that determines when echo is likely to occur, ignoring the first portion of delay and concentrating on when echo is likely. Since the technique concentrates only on the areas where echo will occur, it uses the same amount of processing power even when the echo path delay increases from 32 ms up to 128 ms. Saving processing power Since most of today's echo cancelers don't determine the echo path delay, they must search through the entire echo path, comparing the stored voice against the incoming voice.