AMBE-2000™ Vocoder Chip Users Manual
Version 4.92, June, 08
DVSI Confidential Proprietary, Subject to Change
Page 30
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5.2.3
Framed Input: Word 1 : Control Word 1
Use the 8-bit control word to set various functions.
Table 5-B Control Word 1 Format
Control Word 1 – 8-bits (See Table 1-F)
7: MSB
6
5
4
3
2
1
0 : LSB
Lost Frame
Indicator
Unused
Unused
Unused
Unused
Unused
CNI
Unused
Lost Frame Indicator : Setting the Lost Frame Indicator bit to a 1 will cause the AMBE-2020™ decoder to construct the
voice frame using the parameters from the previous frame. This is an effective way to mask the effects of short periods of
data loss. This bit should be set by the user when channel data is lost or corrupted. It works by replacing the frame of
corrupted data with the previous, intact, frame.
Comfort Noise Insertion (CNI) : Setting the CNI bit will cause the decoder to output a frame of comfort noise. This bit is
used with systems that are capable of discontinuous transmission (DTX).
5.2.4
Framed Input: Words 2-6 : Rate Information
Rate Info 0, Rate Info 1, Rate Info 2, Rate Info 3, Rate Info 4
The initial rate of the AMBE-2020™ is set through the hardware pins RATE_SEL[4-0] (see Section 7.2 and Tables 7-A and
7-B) after resetting the device. The coding rate can be modified for both the encoder and the decoder by sending a framed
packet to the input channel interface. The Rate Selector control field (described in section 5.2.9) determines where to apply
the rate change. Particular attention must be paid to this field when using the BER reporting fields (section 5.3).
The AMBE-2020™ used these five words to set the source and FEC coding rates. Tables 5-C and 5-D list predefined value
for various source and FEC rates. These are only a representation of the most common rates that are requested. Please
contact DVSI for additional rate information if the desired rates are not listed. The software configurations in Table 5-C are
compatible for use with the AMBE-1000™ (using AMBE™ technology). If compatibility is not an issue, use the software
codes in Table 5-D to select speech and FEC rates to optimize use of the AMBE-2020™ (using AMBE+™ technology).
