Echo-Canceller Design Ensures Hands-Free, High-Fidelity Telephony

In the past, system designers programmed general-purpose DSP µPs for high-quality echo cancellation. Now, dedicated hardware eliminates the need for software development, shortens the design cycle, and reduces system cost and power consumption. Echoes during a conversation are the bane of mobile-cellular, cordless, and speaker phones. Echoes are unacceptable in a quality-speech telephone, and you must eliminate them to ensure normal conversation. The causes of echoes include: acoustic feedback from speaker to microphone in a hands-free system; impedance mismatches between a two-wire local loop and four-wire telephone network, causing electrical signals to reflect; and constant, prolonged background noise present in moving vehicles or at public spaces, such as emergency telephones along highways.

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