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Line & Acoustic Echo Canceller Combined

Line & Acoustic Echo Canceller Combined

Line & acoustic echo cancellation is used in applications where both line and acoustic echo are present

A Line & Acoustic Echo Canceller Combined is an echo cancellation solution that is suitable for applications where both types of echoes, line echo and acoustic echo, are present, such as:

  • TDM (PSTN) Telephony
  • VoIP Telephony

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The figure illustrates a high-level configuration of LEC/AEC in the voice network access sub-system of a TDM or VoIP communication network.

In order to perform adequately, the line and acoustic echo canceller combined (LAEC) is expected to have all basic features of line and acoustic echo cancellers and, specifically, be able to fast track echo path changes as well as adequately cover echo path lengths typically present in the acoustical environment such as a conference room, office or meeting room.

In addition to that, the LAEC should be equipped with a non-linear processor that adequately removes residual echoes that cannot be sufficiently cancelled due to rapid changes of echo paths. Additional requirement for the non-linear processor in the LAEC is its ability to remove nonlinear effects caused by nonlinearities of the telephone set’s loudspeaker.

The question of echo canceller coverage of echo paths manifesting in the acoustical environment deserves a separate discussion. Here we only emphasize briefly the presence of three factors that contribute to the acoustic echo that is supposed to be cancelled (or at least mitigated) by LAEC. These are:

  • Direct acoustical coupling between two transducers: loudspeaker and microphone
  • Distinct acoustic reflections (from room walls and other objects) a.k.a., early reflections, of the signal produced by the loudspeaker
  • Sound reverberation caused by large number of acoustic reflections that superimpose on each other, and then gradually attenuate as the sound is absorbed and dissipated while it propagates and interacts with objects in the acoustical environment

The echo path coverage required by LAEC to adequate cancel early reflections in the acoustical environment depends of the size of the room as well as the physical nature of the reflective surfaces.

VOCAL’s Line & acoustic echo canceller combined is reconfigurable and able to cancel both line and acoustic echoes up to 256 ms. Our software can be ported to a variety of DSP processors for customer evaluation. Please contact us to discuss your echo canceller application requirements.

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VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Amherst New York 14228
Phone: +1-716-688-4675
Fax: +1-716-639-0713