ZL38001

The ZL38001 device contains an acoustic echo cancellers, as well as the many control functions necessary to operate the echo canceller. The ZL38001 provides clear signal transmission in both audio path directions to ensure reliable voice communication, even with low level signals. The ZL38001 does not use variable attenuators during double-talk or single-talk periods of speech, as do many other acoustic echo cancellers for speakerphones. Instead, the ZL38001 provides high performance full-duplex operation similar to network echo cancellers, so that users experience clear speech and uninterrupted background signals during the conversation. This prevents subjective sound quality problems associated with "noise gating" or "noise contrasting".

The ZL38001 uses an advanced adaptive filter algorithm that is double-talk stable, which means that convergence takes place even while both parties are talking1. This algorithm allows continual tracking of changes in the echo path, regardless of double-talk, as long as a reference signal is available for the echo canceller. The echo tail cancellation capability of the acoustic echo canceller has been sized appropriately (112 ms) to cancel echo in an average sized office with a reverberation time of less than 112 ms. In addition to the echo cancellers, the following functions are supported:
• Control of adaptive filter convergence speed during periods of double-talk, far end single-talk and near-end echo path changes
• Control of Non-Linear Processor thresholds for suppression of residual non-linear echo
• Howling detector to identify when instability is starting to occur and to take action to prevent oscillation
• Narrow-Band Detector for preventing adaptive filter divergence caused by narrow-band signals
• Offset Nulling filters for removal of DC components in PCM channels
• Limiters that introduce controlled saturation levels
• Serial controller interface compatible with Motorola, National and Intel microcontrollers
• PCM encoder/decoder compatible with /A-Law ITU-T G.711, /A-Law Sign-Mag or linear 2's complement coding
• Automatic gain control on the receive speaker path