TrueSpeech® Co-Processor
PRELIMINARY/CONFIDENTIAL
Version: 1.18
Force NLP:
Force NLP processing to be always activated. This over-rides the NLP/AS/AB control.
NLP Threshold
Scaling:
This field sets the scaling factor (SF) used to calculate the NLP center clipping threshold:
Threshold = Speaker Output signal >> SF
The default SF is 4, so the threshold is calculated by right-shift-by-4 (division by 16)
9.15.6.2
AEC Locked State
In the locked state, the AEC will not undergo further updates of its internal coefficients unless the amount of
instantaneous attenuation measured is greater than the Lock Threshold. This places a significant restriction on the
AEC adaptation control algorithm. It is designed to prevent a hunting effect where the AEC attempts to adapt to
low-level noise instead of to a real echo signal.
Use of this feature is not recommended for echo paths that can vary in real-time. If the echo path changes while the
AEC is in the locked state, the amount of attenuation achieved may never exceed the Lock Threshold. In this
situation, the AEC will never update its internal coefficients.
9.15.6.3
Setting the Lock Threshold
The attenuation threshold at which the AEC enters the locked state is programmable. Use the following command
sequence:
Command Status Response
C1 E014
C2 XXXX
E014
XXXX
where XXXX is the attenuation threshold in dB.
For example, the default threshold is -12 dB and so XXXX = FFF4 (-12 in hexadecimal form).
9.15.6.4
Setting the Un-lock Threshold
The AEC can be programmed to automatically un-lock if the instantaneous measured attenuation indicates that the
AEC is not canceling the echo. This may happen if the echo path was changed.
If the echo path was changed significantly, it is possible that the echo estimate calculated by the AEC is so badly in
error that the AEC creates an effect where it increases the echo signal level instead of reducing it. In this situation,
the AEC can be programmed to automatically un-lock when amplification of the echo signal is detected:
Command Status Response
C1 E01B
C2 XXXX
E01B
XXXX
where XXXX is the attenuation threshold in dB.
For example, the default threshold is +3dB and so XXXX=0003.
Note: When measuring the AEC attenuation, a negative dB value represents a reduction in the output
signal level (attenuation), whereas a positive dB value represents an increase in the output signal
level (amplification).
114
DSP GROUP, INC., 3120 SCOTT BOULEVARD CT8022A11AQC FW Revision 0118
SANTA CLARA, CA 95054 PH: 408 986 – 4300 FAX: 408 986 – 4490
All specifications are subject to change without prior notice.
ETC [ ETC ]
