MT93L16

The MT93L16 device contains two echo cancellers, as well as the many control functions necessary to operate the echo cancellers. One canceller is for acoustic speaker to microphone echo, and one for line echo cancellation. The MT93L16 provides clear signal transmission in both audio path directions to ensure reliable voice communication, even with low level signals. The MT93L16 does not use variable attenuators during double-talk or single-talk periods of speech, as do many other acoustic echo cancellers for speaker-phones. Instead, the MT93L16 provides high performance full-duplex operation similar to network echo cancellers, so that users experience clear speech and un-interrupted background signals during the conversation. This prevents subjective sound quality problems associated with "noise gating" or "noise contrasting".

The MT93L16 uses an advanced adaptive filter algorithm that is double-talk stable, which means that convergence takes place even while both parties are talking 1. This algorithm allows continual tracking of changes in the echo path, regardless of doubletalk, as long as a reference signal is available for the echo canceller.(1. Patent Pending)

The echo tail cancellation capability of the acoustic echo canceller has been sized appropriately (112ms) to cancel echo in an average sized office with a  reverberation time of less than 112ms. The 16ms line echo canceller is sufficient to ensure a high ERLE for most line circuits. In addition to the echo cancellers, the following functions are supported:
• Control of adaptive filter convergence speed during periods of double-talk, far end singletalk, 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 m/ALaw ITU-T G.711, m/A-Law Sign-Mag or linear 2's complement coding.
• Automatic gain control on the receive speaker path.