Acoustic echo canceller targets hands-free communication systems -

Acoustic echo canceller targets hands-free communication systems


The first in a family of voice processing chips from Zarlink Semiconductor is aimed at improving voice quality and reducing noise in hands-free communication devices. In addition to the automobile, hands-free technology is a key requirement in a wide range of communication systems, such as security networks, desktop phones, conference phones, and PDAs.

Hands-free communication systems are often hindered by acoustic echo that is created when the voice from the loudspeaker in a car kit or conference phone, for example, is picked up by the microphone and retransmitted. Mobile network delays also make acoustic echo more noticeable. To compensate, hands-free systems previously used lower performance voice processing technologies that supported only half-duplex operation. Half-duplex means only one person can speak at a time, resulting in an unnatural, stilted conversation.

In comparison, Zarlink's ZL38002 uses an advanced adaptive algorithm that constantly tracks and reduces background noise while preserving voice quality. Voice signals are transmitted in both directions, allowing natural two-way conversation, even when signal levels are low. The ZL38002 chip utilizes an advanced non-linear process design supporting full-duplex speech with no switched loss of the signal path. Zarlink's algorithm design operates during double-talk situations when both callers are speaking at the same time.

Hands-free system microphones also pick up background noise, such as an accelerating car engine and tire noise, which further degrades voice quality. The ZL38002's acoustic echo canceller technology is specifically designed to deliver exceptional performance in high background noise environments.

Programmable noise reduction allows the user to adjust the noise cancellation level to meet system requirements without distorting the audio signal. The ZL38002 acoustic echo canceller integrates other advanced features to ensure high sound quality, including anti-howling detection that identifies instability in the audio path and automatically takes preventative measures to avoid oscillation.

The ZL38002 device is now available in a 36-pin QSOP (quarter small outline package) and 48-pin TQFP (thin quad flat package), measuring 7 by 7 mm. Lead-free package options are also available. An evaluation board, hands-free car kit application board, and API software are available. In quantities of 1000, the device sells for $5.50. For more information, visit

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