Integrating an echo canceller into a packet based or frame-based system requires special timing considerations. A realistic source of electrical echo in a telephone system exhibits diffusion. By this I mean that the impulse response of the echo source (the echo tail) is not an impulse. The amplitude of the echo tail is non-zero for a period of time known as the tail length. The compensation for this delay is shown between the far end and the echo canceller. There are two packet buffers in a delay-line fashion. This results in a two-frame delay of the inbound far end signal into the echo canceller.
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