User`s manual

AMBE-2000™ Vocoder Chip
User’s Manual Version 4.9
DVSI Confidential Proprietary, Subject to Change Page 61
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1111 Most confident 1
Placing a logic high on pin 79 of either the AMBE-2000™ or AMBE-2020™ vocoder chips enables the soft
decision error correction on the decoder. Enabling the soft-decision does nothing to the encoder packet. The packet
will look like a normal encoded packet. The user must implement circuitry at the receive end of the channel for
making a finer (4 bit) estimation of the received energy (see above link for an explanation of how this can be done).
The AMBE-2000™/2020 decoder packet structure is altered. The decoder expects each voice data bit of the
encoded packet to be represented by 4 soft decision (SD) bits. The decoder will make the decision of whether or not
a 1 or a 0 is represented by the SD bits. Table 1 is an example of a soft-decision decoder packet.