Sparse Models in Echo Cancellation: When the Old Meets the New
Yannis Kopsinis, Symeon Chouvardas, Sergios Theodoridis · 2015
Echo cancellation, which is a key ingredient towards high-quality communications, appears to be a very challenging filtering task due to a number of inherent peculiarities. Figure 6.1 depicts a schematic representation of the echo cancellation problem. In an ideal communication setting, the loudspeaker at the far-end would either exclusively transmit the voice of the person at the near-end or nothing if this person is silent. This should be the case irrespective of whether the person at the far-end is speaking or not. However, in realistic conditions, this is not true; the far-end speech signal travels through the communication channel and it is transmitted via the loudspeaker in the near-end room. Due to the room impulse response and delays in the communication line, the microphone at the near-end captures a filtered version of the far-end speech, which is transmitted back to the far-end in the form of annoying echo. In wired communications, even when a room is not involved in echo generation, known as acoustic echo, electrically induced echo appears due to unbalanced coupling between the 2-wire and 4-wire circuits. The echo cancellation task aims at estimating the impulse response corresponding to the echo path. Doing so, the echo can be reproduced at the far-end and be subtracted from the received signal. In this way, the received signal is cleansed from the echo before its transmission through the loudspeaker.