What are three parts of echo canceller? Explain each part in detail.
Answers
Stereo Acoustic Echo Canceller (AEC)
A Stereo Acoustic Echo Canceller (SAEC) is one example of multichannel acoustic echo cancellation operations where the channels are highly correlated. Stereo AEC devices are an important part of telecommunication systems where the end users are located in conference rooms or auditoria equipped with stereophonic and/or surround sound systems.
The Acoustic Echo Canceller
The Acoustic Echo Canceller is designed for removing/suppressing acoustic reflections, whereas line/network echo cancellers primarily address echo signals produced by reflections from hybrid circuits (or transformers) converting 4-wire interface into 2-wire interface in POTS/PSTN systems.
Characteristics of the reflected acoustic signals are as follows:
Relatively long echo span (a.k.a. echo tail), often exceeding 160ms;
Wider range of echo signal levels, often extending over high signal levels (thus corresponding to low ERL values, reaching negative values in some configurations);
Frequent changes of echoes (illustrated by variations of echo path impulse responses), according to position of the voice terminal and/or speaker with respect to reflecting objects in the near-end room;
Due to nonlinear behavior of the loudspeaker, the relationship between the acoustic pressure produced by the loudspeaker and the electrical signal driving it is not exactly linear; therefore, an adaptive filter that, in most designs, is a linear component, cannot adequately model the echo path. As a result, more stringent requirements are imposed onto the NLP so any audible traces of residual echoes are removed.