Specifications

Net-2000™ VCU Users Manual

Version 4.0, December, 2013

IP Mode

Echo

Canceller is available with the following vocoders:

Vocoder

AMBE®

AMBE+™

AMBE+2™

APCO Enhanced

GMR-1

GMR-2

BGAN Vocoder

GMR-2+ Vocoder

4.9.5 DTX (BGAN and GMR-2+ Vocoders Only)

The Discontinuous Transmission (DTx) feature is used in conjuction with VAD. It can be used to reduce transmit

power during times of conversational silence. When DTx is checked (DTX_ENABLE=1), the encoder will output a

silence frame (in-band) whenever the speech data is determined to be background noise or silence.

This silence frame contains information regarding the level of background noise, which allows the corresponding

Net-2000’s decoder to synthesize a “Comfort Noise” signal. The comfort noise is intended to give the listener the

feeling that they are still connected, as opposed to producing absolute silence, which can give the impression that,

the connection has been “dropped”.

To ensure the smoothest audible transitions between synthesized speech and synthesized silence, DVSI recommends

the user to send a silence frame with background noise level parameters to the decoder approximately every 500-

1000 milliseconds. The encoder and decoder expects that most silence frames will be discarded and that only an

occasional silence frame (approximately one per second) may be transmitted to update the CNI state at the decoder.

When DTX is not checked (DTX_ENABLE=0), the encoder does not output special silence frames when silence is

detected.

DTx is available with the following vocoders:

Vocoder

BGAN Vocoder

GMR-2+ Vocoder

4.9.6 Automatic Gain Control (APCO Enhanced Vocoder Only)

The Automatic Gain Control (AGC) attempts to amplify or attenuate the incoming signal to maintain a relatively

constant voice level. The applied gain is limited to [+20,-10] dB. Automatic Gain Control is available with the

following vocoders:

Automatic Gain Control detection is available with the following vocoder:

Vocoder

APCO Enhanced

4.9.7 High Pitch Detection Feature (GMR-2+ Vocoder Only)

When checked (enabled) High Pitch Detection (HPD) increases the pitch range of the vocoder in order to

accommodate voices with an especially high pitch voice. The vast majority of speakers do not exceed the vocoder’s

typical pitch limits. In very rare cases when HPD is required it may be enabled.

(Subject to Change) Page 24

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