Used in speakerphones and videoconferencing to eliminate echoes caused by microphones capturing sounds they already produced. Echo cancellation works by "remembering" what signal has been put through the speaker, and then subtracting it, appropriately attenuated and delayed, from the signal entering the microphone. The difficulty is in attenuating and delaying the correct amount. Echo cancellation requires much computationto perform the cancellation algorithms, and this processor capability requirement adds to the cost.