Digital Voice Systems VC-20-MR2, Руководство пользователя

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Section 1- Product Introduction
VC-20 AMBE™ Vocoder Board User’s Manual
page 1
The Speech Compression Specialists
D
IGITAL
V
OICE
S
YSTEMS,
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NC.
1 Product Introduction
1.1 General Information
The Digital Voice Systems, Inc. (DVSI) VC-20-MR2 voice codec is a full-duplex
real-time voice processing board. The VC-20-MR2 contains
proprietary software
which implements the Advanced Multi-Band Excitation (AMBE™) voice coding
algorithm. DVSI grants a license to its customers to use this software according to
the terms established in the attached
AMBE™ Software END USER License
Agreement . Use of the VC-20-MR2, or any portion thereof, signifies acceptance of
these licensing terms.
The VC-20-MR2 operates by digitizing an analog speech signal using an on-board
A-to-D converter. This digitized speech is then processed by the encoder and
converted into a 4.8/2.4 kbps data bit stream. This bit stream is output to a modem
or similar device. Simultaneously, the VC-20-MR2 receives a 4.8/2.4 kbps data bit
stream from a modem or similar device. This received bit stream is processed by
the decoder and converted into a synthetic speech signal which is then converted
into an analog signal using the on-board D-to-A converter. The encoder and
decoder are fully asynchronous.
The VC-20-MR2 (4800bps) has been designed to be robust to both acoustic
background noise and channel errors. It generally contains sufficient channel error
protection to produce high quality speech at bit error rates up to 1-2% and
intelligible speech at bit error rates up to 4-5%.
The VC-20-MR2 (2400bps) has been designed to be robust to acoustic background
noise and limited channel errors. The VC-20-MR2 (2400) will produce intelligible
speech at bit error rates up to 1-2%.
The VC-20-MR2 includes a number of advanced features such as an
automatic Voice/Silence detection (VAD), adaptive comfort noise
generation, DTMF detection and signaling, soft-decision decoding, frame
stealing support and echo cancellation. Operation of these features is
described in the following sections. The VC-20-MR2 is also capable of
supporting optional features such as external codecs and downloading