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Recording and Playback
•It does not make sense to use the same DTMF digit as a termination condition on a play and as
the pause/resume condition.
•To end a paused play, use dx_stopch().
8.12 Echo Cancellation Resource
The echo cancellation resource (ECR) feature is not supported on DM3 boards.
The echo cancellation resource (ECR) feature is a functional component of a voice channel. ECR is
discussed in more detail in the following topics:
•Overview of Echo Cancellation Resource
•Echo Cancellation Resource Operation
•Modes of Operation
•Echo Cancellation Resource Application Models

8.12.1 Overview of Echo Cancellation Resource

The ECR feature lets you use echo cancellation on signals external to the voice channel. The echo
cancellation capability becomes a system-wide resource that may be applied to any time-division
multiplexing (TDM) bus PCM stream. The addition of the ECR feature allows the application to
dynamically configure a voice channel as either an echo cancellation device (ECR mode) or as a
standard voice processing channel (SVP mode). In ECR mode, the voice channel can dynamically
perform echo cancellation on any TDM bus time slot signal external to the voice channel. In ECR
mode, a portion of the standard voice functionality remains available while another portion of it
becomes unavailable.
Note: The ECR feature has been replaced with the continuous speech processing (CSP) API. CSP is the
preferred method for echo cancellation and should be used where available. For more information,
see the Continuous Speech Processing API Programming Guide and Continuous Speech
Processing API Library Reference.
Prior to the implementation of the ECR feature in the voice library, each voice channel device had a
single transmit (TX) TDM bus time slot assigned to it for data communication across the TDM bus.
To connect one device to another across the TDM bus, an application would call xx_listen()
(where xx_ is ag_, dt_, dx_, or ms_) on one voice or network device to connect to a second device’s
transmit channel. Any signal transmitted by the second device on its transmit channel (TX channel)
would be received by the first device’s receive channel (RX channel). For a full-duplex connection,
the second device would then call xx_listen() to connect its receive channel to the first device’s
transmit channel.
Throughout this section, reference is made to echo cancellation-specific terminology. See the
glossary for definitions of ECR terminology.