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Voice API for Windows Operating Systems Library Reference — November 2003 283
modify characteristics of the echo canceller — dx_listenecrex( )
dx_listenecrex( )
modify characteristics of the echo canceller
!
!!
! Description
The dx_listenecrex( ) function performs identically to dx_listenecr( ) and also modifies the
characteristics of the echo canceller. The characteristics of the echo canceller can be set using the
DX_ECRCT structure. For more information on this structure, see DX_ECRCT, on page 508.
Note: The ECR functions have been replaced by the continuous speech processing (CSP) API functions.
CSP provides enhanced echo cancellation. For more information, see the Continuous Speech
Processing API Programming Guide and Continuous Speech Processing API Library Reference.
One characteristic of the echo canceller that can be set using dx_listenecrex( ) is non-linear
processing (NLP). When NLP is activated, the output of the echo canceller is replaced with an
estimate of the background noise. The NLP provides full echo suppression as long as the echo-
reference signal contains speech signals and the echo-carrying signal does not. In this case, the
echo canceller cancels the echo and maintains the full duplex connection.
Note: Disable NLP when using the echo canceller output for voice recognition algorithms as NLP may
clip the beginning of speech.
!
!!
! Cautions
This function fails when:
Name: int dx_listenecrex(chdev, sc_tsinfop, ecrctp)
Inputs: int chdev
• handle of voice channel device on which echo cancellation will
be performed
SC_TSINFO *sc_tsinfop
• pointer to TDM bus time slot information structure
DX_ECRCT void *ecrctp
• pointer to ECR characteristic structure
Returns: 0 on success
-1 on error
Includes: srllib.h
dxxxlib.h
Category: Echo Cancellation Resource
Mode: synchronous
Platform: Springware
Parameter Description
chdev specifies the voice channel device handle obtained when the channel was
opened using dx_open( )
sc_tsinfop specifies a pointer to the SC_TSINFO structure
ecrctp specifies a pointer to the DX_ECRCT structure cast to a (void *)