Cirrus Logic CS6422 - Manual (Page 27)

CS6422
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3.8.1 HWLD - HOWL DETECTOR DISABLE
This is a diagnostic parameter that is normally set to ‘0’.
In normal operation, the CS6422 will clear both the AEC and NEC coefficients, dropping the device
into half-duplex operation, whenever an instability event is detected. Such an event can be caused
by excessive loop gain, a major path change, or mistraining of the echo cancellers.
Setting HwlD to ‘1’ prevents the instability detector from clearing the echo cancellers’ coefficients.
3.8.2 TD - TONE DETECTOR DISABLE
This is a diagnostic parameter that is normally set to ‘0’.
In normal operation, the tone detector responds to the detection of tones in the receive path. If the
CS6422 is in half-duplex mode, the tone detector will clear the AEC coefficients and force the half-
duplex engine into <Receive> mode to allow the tone to pass through, independent of the presence
of signals at the near-end microphone.
If the CS6422 is in full-dulpex mode when a tone is detected, the tone detector will momentarily freeze
the AEC coefficients to prevent false training.
3.8.3 APCD - ACOUSTIC PATH CHANGE DETECTOR DISABLE
This diagnostic bit is normally set to ‘0’.
The purpose of the acoustic path change detector is to respond to drastic path changes by clearing
the AEC coefficients to facilitate rapid and accurate convergence to the new path.
Disabling the acoustic path change detector prevents it from clearing the AEC coefficients, thus forc-
ing the filter to ‘adapt out’ of the path change, which typically takes longer and is less accurate than
adapting from a cleared state.
3.8.4 NPCD - NETWORK PATH CHANGE DETECTOR DISABLE
This diagnostic bit is normally set to ‘0’.
The purpose of the network path change detector is to respond to drastic path changes by clearing
the NEC coefficients to facilitate rapid and accurate convergence to the new path.
Disabling the network path change detector prevents it from clearing the NEC coefficients, thus forc-
ing the filter to ‘adapt out’ of the path change, which typically takes longer and is less accurate than
adapting from a cleared state.
3.8.5 APFD/NPFD - ACOUSTIC PRE-EMPHASIS FILTER DISABLE/NETWORK PRE-EMPHASIS
FILTER DISABLE
These diagnostic bits are normally set to ‘0’.
The pre-emphasis filter helps the adaptive filter correctly model the coupling path by attenuating lower
frequency information. This is done because high-frequency information more accurately describes
the echo path, that is, low frequency information is more spatially ambiguous.
Sometimes it is useful to disable the pre-emphasis filter when performing ERLE tests using white
noise, since the filter will tend to prevent the adaptive filter from cancelling the low frequency compo-
nents of the signal, resulting in artificially low ERLE measurements.
CS6422
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