TrueSpeech® Co-Processor
PRELIMINARY/CONFIDENTIAL
Version: 1.18
Large duration (> 100ms) multi-path echoes can be handled using echo cancellers with very long filter lengths (512-
1024 tap filters) or using multiple sub-band (frequency division) techniques. This approach tends to require
significant computation and processing resources resulting in a relatively high-cost solution.
In cost sensitive applications, acoustic type echoes are more appropriately handled using techniques like NLP and
AS/AB together with some degree of Echo Suppression.
High background noise levels and non-linear echo paths tend to reduce the amount of echo cancellation achieved,
thus requiring increased reliance on the NLP/AS/AB features to compensate.
C1
S1
C2
S2
C1
S1
C2
S2
C1
S1
C2
E011H
E011H
0100H
0100H
E013H
E013H
0002H
0002H
E012H
E012H
0023H
Set NLP threshold floor
Use higher threshold floor value
Set Attenuation Scaling
Set attenuation scale factor to x2
Train & Lock Command
NLP threshold = Speaker Output >> 3 (divided by 8)
NLP Mode = 1, activate NLP/AS based on measured AEC attenuation
S2
0023H
C1
S1
C2
S2
E014H
E014H
0003H
0003H
Set lock threshold (used to activate NLP/AS)
Set threshold to 3dB measured attenuation
Example: Telephone Echo environment (local 2-to-4 wire hybrid provides 6-12 dB or cancellation - large amplitude
echoes).
C1
S1
C2
S2
C1
S1
C2
S2
C1
S1
C2
E011H
E011H
0080H
0080H
E013H
E013H
0002H
0002H
E012H
E012H
0024H
Set NLP threshold floor
Use lower threshold floor value
Set Attenuation Scaling
Set attenuation scale factor to x2
Train & Lock Command
NLP threshold = Speaker Output >> 4 (divided by 16)
NLP Mode = 1, activate NLP/AS based on measured AEC attenuation
S2
C1
S1
C2
S2
0024H
E014H
E014H
0006H
0006H
Set lock threshold (used to activate NLP/AS)
Set threshold to 6dB measured attenuation
110
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 ]
