TrueSpeech® Co-Processor
PRELIMINARY/CONFIDENTIAL
Version: 1.18
The NLP threshold is set dynamically relative to the output signal amplitude (in CT8020 devices, the NLP threshold
was set relative to the input (echo) signal). The minimum NLP threshold is controlled by setting the NLP threshold
floor:
NLP threshold = output signal * scale factor (1/16)
if NLP threshold < NLP threshold floor, then NLP threshold = NLP threshold floor.
The NLP threshold floor is set using the following command:
C1
S1
C2
S2
E011H
E011H
XXXXH
XXXXH
where XXXX is the NLP threshold floor. Recommended values are 0080H or 0100H.
The output signal scale factor can be adjusted using the additional control bits in the AEC train and lock command.
This command may be sent at any time.
To disable NLP use the following command
C1
S1
C2
S2
E011H
E011H
FFFFH
FFFFH
9.15.5.2
Attenuation Scaling (AS) & Attenuation Boost (AB)
Attenuation Scaling (AS) is a technique that allows the CT8022 to increase the amount of echo attenuation achieved
when dealing with acoustic echoes in environments which prevent the AEC canceller from fully training. One
example of this is environments with high background noise levels or significant non-linear distortion in the echo
path.
The dynamic Attenuation Scaling mechanism measures the amount of cancellation attenuation (in dB) produced by
the AEC canceller, scales this attenuation, and then adds attenuation (suppression) equal to the scaled attenuation to
the cancelled echo signal.
For example, if the AEC measures 6dB of attenuation due to the canceller, and the scale factor is set to 2, then the
Attenuation scaling adds 6*2 = 12dB of attenuation (suppression).
The Attenuation Scaling mechanism can also be operated in fixed Attenuation Boost (AB) mode where a fixed
amount of extra attenuation (suppression) is added.
To set the Attenuation Scaling mode, use the following command:
C1
S1
C2
S2
E013H
E013H
XXYYH
XXYYH
For fixed scaling, set XX=fixed attenuation, and set YY=00. For example, 0600H selects 6dB of fixed Attenuation
Boost. Valid values for XX are 0,6,12,18, etc., in steps of 6dB
For dynamic Attenuation Scaling set YY= attenuation scaling factor and XX=00. For example 0002H sets
attenuation scaling with a scale factor of 2. Valid range for YY is 0-10.
This command may be sent at any time.
108
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 ]
