TrueSpeech® Co-Processor
PRELIMINARY/CONFIDENTIAL
Version: 1.18
9.15
Acoustic Echo Canceller In DSVD Mode
It is possible to use the Acoustic Echo Canceller (AEC) to cancel echoes in the input signal during full-duplex
(DSVD) speech mode. It is possible to use it when only playback is in operation to remove playback echoes from
the signal input to the DTMF and Call Progress Tone Detectors. When used to cancel playback-only echoes, it is
recommended that the Echo Suppressor (loop attenuation) feature and Advanced AEC feature be disabled. For the
AEC to function, both an outgoing (playback) and incoming (for record or tone detection) audio data stream are
necessary. When the AEC is operating, the Automatic Gain Control (AGC) feature (available in conjunction with
record mode) should be de-activated. However, the playback and record level controls are still available when the
AEC is active. Care must be taken when setting the record and playback levels so as not to compromise operation of
the AEC. The purpose of the AEC is to reduce, as much as possible, the acoustic echo of the outgoing speech
(playback) reflected from the speaker into the microphone (record speech stream). Increasing the playback or
record volumes will increase the level of audible echo. Note that the record level setting does not affect the signal
level input to the tone detectors.
The AEC is switched On or Off using the following commands.
Command:
Status:
B001H
B001H
AEC on
Command:
Status:
B002H
B002H
AEC off
These commands can be issued at any time, but the AEC will only be active when playback is active (otherwise there
is no echo to cancel).
The commands Get Speakerphone Status, Set Speakerphone Parameters (speaker and line volume and loop
attenuation), and Speakerphone Configuration (loop adjustment mode) can be used to control the AEC. Refer to
Section 9.21 for detailed descriptions of these commands.
The Speakerphone commands listed above only work when record and/or playback are already active. Sending
these commands when the CT8022 is in IDLE mode will cause improper entry to standalone Speakerphone mode.
Attempting to train the Electrical Echo Canceller (EEC) in DSVD speakerphone mode is not permitted. The EEC is
used only in standalone Speakerphone mode to cancel the stationary (fixed, non-varying) electrical signal echo from
the telephone line (via the second, optional, CODEC0).
Use the following sequence of commands (from IDLE mode):
Start Playback and/or Start Record
1. AEC on
2. Set Speakerphone Parameters
3. optional - Speakerphone Configuration
4. optional - Get Speakerphone Status
100
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 ]
