Version: 1.18
PRELIMINARY/CONFIDENTIAL
TrueSpeech® Co-Processor
9.15.9
Reading the Instantaneous AEC Attenuation
The Host can read the approximate instantaneous attenuation as measured internally by the AEC using the following
command:
Command
Status response
E00A
XXXX
where XXXX is the approximate attenuation in dB. This can be a negative value that indicates the current
instantaneous echo signal is being attenuated, or a small positive value indicating that either the AEC is not trained,
or that no input or echo signal is present. If the attenuation value read is a positive value larger than +6dB, this
indicates that the AEC is operating under adverse or error conditions.
The value read can only show a significant negative value (indicating a significant amount of attenuation) when a
speaker output signal is present which causes a large input echo. When no input signal is present, the amount of
attenuation achieved is indeterminate.
Note that the reported attenuation is the difference in signal level between the microphone input signal and the echo-
cancelled microphone input signal. It is not the difference between the speaker output and the echo-cancelled
microphone input signal. Any attenuation provided by the external echo path is not included in the reported
attenuation. Example: if the echo path returns an echo -20 dB relative to the output signal, and the AEC succeeds in
canceling a further 6dB of echo, then the reported cancellation is -6dB (not -26dB which is the overall cancellation
attenuation). Further, the reported AEC cancellation does not include the effect of the NLP/AS/AB feature). The
reported cancellation is the cancellation effect due to the CT8022 AEC only.
9.15.10 Saving and Restoring the AEC and EEC Coefficients
The current AEC and EEC echo estimation filter coefficients can be saved and restored to the external data SRAM
attached to the CT8022 device. Coefficients saved in the external SRAMs are never lost except in the case of a
power on-off cycle. The coefficients saved are not affected by a device reset. The coefficients will be lost if the
external SRAM self test command is used.
The working filter coefficients of the AEC and EEC are reset each time the echo canceller is restarted. In the case of
the AEC, the filter coefficients are reset by an AEC-off, AEC-on sequence.
9.15.10.1 Save AEC Coefficients
Command
Status
E016
E016
9.15.10.2 Restore AEC Coefficients
Command
Status
E017
E017
9.15.10.3 Save EEC Coefficients
Command
Status
E018
E018
9.15.10.4 Restore EEC Coefficients
Command
Status
E019
E019
CT8022A11AQC FW Revision 0118 DSP GROUP, INC., 3120 SCOTT BOULEVARD
SANTA CLARA, CA 95054 PH: 408 986 – 4300 FAX: 408 986 – 4490
117
All specifications are subject to change without prior notice.
ETC [ ETC ]
