AMBE-2000™ Vocoder Chip

User’s Manual Version 3.0

page 26

Confidential Proprietary, Subject to Change

5.2.3 Formatted 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-2000™ 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 Formatted Input : Words 2-6 : Rate Info 0, Rate Info 1, Rate Info 2, Rate Info 3,

Rate Info 4

The initial rate of the AMBE-2000 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 then be modified for both the encoder and the decoder through the Unformatted

channel interface. The Rate Selector control field (describe in section) determines where to apply the rate change.

The AMBE-2000 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. The software configurations in Table 4-C are compatible for use with the AMBE-1000™. If

compatibility is not an issue, use the software codes in Table 4-D to select speech and FEC rates to optimize use of the AMBE-

2000™.

Table 5-C Rate Selection Using Rate Info 0-4, compatible w/ AMBE-1000™

Rate Info 0

Rate Info 1

Rate Info 2

Rate Info 3

Rate Info 4

Speech Rate

(bps)

FEC Rate

(bps)

Total Rate

(bps)

0x9030

0x0000

0x0000

0x0000

0x4330

2400

0

0x902f

0x0000

0x0000

0x0000

0x6930

2350

50

2400

0x9348

0x0000

0x0000

0x0000

0x6f48

3600

0

0x9243

0x0080

0x0000

0x0000

0x5348

3350

250

3600

0xab50

0x0000

0x0000

0x0000

0x3950

4000

0

0x934b

0x0080

0x0000

0x0000

0x3950

3750

250

4000

0xab60

0x0000

0x0000

0x0000

0x7960

4800

0

0xab5b

0x0080

0x0000

0x0000

0x6860

4550

250

0x9348

0x2030

0x0000

0x0000

0x7060

3600

1200

0x923e

0x2800

0x0000

0x0000

0x7460

3100

1700

4800

0xab53

0x2c00

0x0000

0x0000

0x5680

4150

2250

6400

0xab58

0x3000

0x0000

0x0000

0x4490

4400

2800

7200

0xbf9b

0x0080

0x0000

0x0000

0x49a0

7750

250

0xab5d

0x3400

0x0000

0x0000

0x31a0

4650

3350

8000

0xbfc0

0x0000

0x0000

0x0000

0x72c0

9600

0

0xab16

0xe400

0x0000

0x0000

0x67c0

4850

4750

9600