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4.1Algorithm Tables (Program Space)

This section has 849 words and contains six tables. The variables of the involved variables have their format described in Table 30. These tables are:

1.RAM initialization table, INIRAM. This table contains reset values of internal processing variables, and constant values that are transferred in RAM when applying the coder reset routine, _G726ENC_TI_reset or _G726DEC_TI_reset.

2.|I| tables for all rates. Each table contains successively:

a.The lowest level of input quantizer interval, QS|I| (first value of column two, Table 12 through Table 15).

b.The output level of the inverse quantizer, DQLN|I| (column three, Table 16 through Table 19).

c.The rate-of-change weighting function, F|I|, (Table 20 through Table 23).

d.The scale-factor multipliers, W|I| (Table 24 through Table 27).

3.Quantizer tables for all rates. Each table gives the output word that corresponds to a certain level of quantization. For the encoder, it gives the ADPCM word I (in two’s complement, column three of Table 12 through Table 15), and for the decoder (in re-encoding routine for synchronous adjustment), it gives the word ID (in absolute value, column four of Table 12 through Table 15), which has to be compared with the original ADPCM code.

4.Inverse quantizer tables for all rates. Each table gives, from a I ADPCM code, the output level of the quantizer which corresponds to the quantized difference signal (normalized and in logarithmic format, column three, Table 16 through Table 19). It also gives the sign of this quantized difference (column two, Table 16 through Table 19). This sign, which is also the sign of I, is the sign of the original difference signal before being normalized and going into logarithmic domain. Lastly, it gives the word the magnitude of I (column four of Table 16 through Table 19), which has to be compared with ID (see Table 12 through Table 15).

5.A-law and m-law tables for PCM expanding. This inverse quantizer table gives the linear PCM level corresponding to a logarithmic PCM code (see section 3.1.2).

6.PCM laws and coder rate selection tables. These tables permit the initialization of the coder, based on linear PCM, A-law PCM, or m-law PCM choice, and 16, 24, 32, or 40 Kbps coding choice. The relevant variables are those of Table 9.

Table 12. Quantizer Definition for 40-Kbps ADPCM

NOTE: The I values are transmitted with bit 1.

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Table 13. Quantizer Definition for 32-Kbps ADPCM

NOTE: The I values are transmitted with bit 1.

Table 14. Quantizer Definition for 24-Kbps ADPCM

NOTE: The I values are transmitted with bit 1.

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Table 16. Quantizer Output Levels for 40-Kbps ADPCM (Continued)

NOTES: 1. The I values are received, starting with bit 1.

2.It is possible for the decoder to receive the codeword 00000 because of transmission disturbances (e.g., line bit errors).

Table 17. Quantizer Output Levels for 32-Kbps ADPCM

NOTES: 1. The I values are received, starting with bit 1.

2.It is possible for the decoder to receive the codeword 00000 because of transmission disturbances (e.g., line bit errors).

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NOTES: 1. The I values are received, starting with bit 1.

2.It is possible for the decoder to receive the codeword 00000 because of transmission disturbances

(e.g., line bit errors).

Table 18. Quantizer Output Levels for 24-Kbps ADPCM

NOTES: 1. The I values are received, starting with bit 1.

2.It is possible for the decoder to receive the codeword 000 because of transmission disturbances (e.g., line bit errors).

Table 19. Quantizer Output Levels for 16-Kbps ADPCM

NOTE: The I values are received, starting with bit 1.

Table 20. Map Quantizer Output F|I| for 40-Kbps ADPCM

Table 21. Map Quantizer Output F|I| for 32 Kbps ADPCM

44 G.726 Adaptive Differential Pulse Code Modulation (ADPCM) on the TMS320C54x DSP

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