Intel 52377002 8.12.3 Modes of Operation

104 Voice API Programming Guide — June 2005

Recording and Playback

8.12.3 Modes of Operation

The echo cancellation resource feature has two modes of operation as discussed in the following

topics:

•Overview of Modes

•Standard Voice Processing (SVP) Mode

•Echo Cancellation Resource (ECR) Mode

When the ECR feature is enabled at initialization time on a supported board, there are two possible

modes of operation: SVP and ECR. Until ECR mode is activated, the board operates in the

Standard Voice Processing (SVP) mode, which offers default echo cancellation. The ECR mode,

which provides high-performance echo cancellation, can be dynamically activated or deactivated

on any voice channel of the enabled board.

To enable ECR mode, set EC_Resource to ON in the .cfg file or in the configuration manager

(DCM) (Windows only) when configuring the board.

All voice channels are initially in the SVP mode with the default echo cancellation for ECR

feature-enabled boards. The SVP mode utilizes a 48 tap (6 ms) echo canceller. In SVP mode, all

voice functions operate as usual, with one exception. If a channel in SVP mode is playing a file and

listening (via a dx_listen( ) function), then playback transmits data on both the standard voice-

transmit time slot and the echo-cancellation transmit time slot. The standard voice-transmit time

slot carries the play signal. The echo cancellation time slot carries an echo-canceled version of the

signal from the receive time slot. This echo-canceled signal is derived from the original play signal

(the echo reference) and the signal from the receive time slot specified in the dx_listen() function

(the echo carrying signal).

Any voice channel can be placed into ECR mode via the dx_listenecr() or dx_listenecrex( )

function on an ECR feature-enabled board. When a voice channel is placed in ECR mode, the echo

reference TDM bus time slot is specified and the high performance echo canceller is activated. The

ECR mode supplies 128 tap (16 ms) echo cancellation.

When an echo carrying signal is provided as an input to the ECR by an associated dx_listen()

function, an echo-canceled version of that signal is produced on the echo-cancellation TDM bus

time slot. If no echo carrying signal is defined, the contents of the echo-cancellation transmit time

slot are undefined and unpredictable. Other characteristics of the echo canceller can be set if the