User`s guide

Dialogic
®
System Release 6.0 PCI for Windows
®
Release Update, Rev 62 — January 30, 2008 236
Dialogic Corporation
Dialogic
®
D/41JCT-LS Media Boards, and all other JCT Boards that use a continuous
speech processing firmware load, function with single echo canceller convergence by
default. Therefore it is not necessary to use the ECCH_CONVERGE channel parameter
with these boards.
1.63.1 Feature Description
Speech-enabled applications that re-enable continuous speech processing and have loud
prompts experience bursts of excessive echo in the streamed audio on each play file,
causing application malfunction. These excessive echo bursts are caused by continuous
echo canceller (EC) convergence, which is re-initialized and re-converges on each new
ec_stream( ) function. This results in several hundred milliseconds of excessive play echo
at the beginning of each play file, which confuses the host-based recognizer, degrading
the operation of the application system.
Single EC convergence can help with this problem. With single EC convergence, the
addressed echo canceller will converge once, after the first ec_stream( ) function is
issued, and from then on the convergence coefficients are saved for the subsequent
ec_stream( ) functions. The echo canceller should be set to re-converge on the first call to
ec_stream( ) of each new phone call. This provides consistent echo cancellation and
optimized barge-in performance.
The following sections describe how single EC convergence works on DMV160LP and
JCT Boards.
1.63.1.1 Single EC Convergence for DMV160LP Boards
Using the new channel parameter, ECCH_CONVERGE, you can switch from continuous
to single EC convergence. ECCH_CONVERGE can take a value of ON or OFF. The
default value is ON (continuous EC convergence), which means that the echo canceller
will re-converge, or retrain, on every new call to ec_stream( ). The ECCH_CONVERGE
parameter supports applications that issue a new ec_stream( ) function with each play
file. This echo convergence mode setting is unaffected by the ec_stopch( ) function.
Note: These parameter operations cannot be issued when any voice I/O function is active on
that channel. A TDX_BUSY error will be returned if it is attempted.
Single EC convergence is set for DMV160LP Boards as follows:
1. At the beginning of each new phone call, the application must set ECCH_CONVERGE
to ON to allow the echo canceller to adapt to the connected trunk's characteristics.
2. Immediately after the first ec_stream( ) for the phone call, set the ECCH_CONVERGE
to OFF.
3. Reset ECCH_CONVERGE to ON for the next phone call.
4. After the first ec_stream( ), set ECCH_CONVERGE to OFF.