nchanges.txt

语音编解码算法G.723.1的C语言算法原代码

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File : nchanges.txt
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        This file contains all the changes between v3.0 and v4.1
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1) Function Vec_Norm() was modified to return the number of shifts
        performed.
                FILES Modified : util_lbc.c util_lbc.h

2) Function Durbin() was modified to return the prediction error value.
                FILES Modified : lpc.c lpc.h

3) The 16 bit CRC indicator was excluded from the final bit stream.
        In order to use CRC one should generate additional file, with
                one word per frame CRC marks, 0 ok, 1 Fer. Addtional command
                line switch -fName was added to the main.
        FILES Modified : lbccodec.c decod.c decod.h

4) The new bit packing procedure for both rates was added. Notice that this
new bitstream does not need to be swapped.

5) Preparation for VAD inserted.

6) Four bugs have been corrected.
        modified routines:
                Comp_Lpc in file lpc.c
                Find_Acbk in file exc_lbc.c
                Find_Best in file exc_lbc.c
                Spf in file lpc.c

7) Include some typdef definition for the VAX system
        ===> done in file typedef.h

8) Rename the functions
        Rand as Rand_Lbc
        Read as Read_Lbc
        Write as Write_Lbc
        Sqrt as Sqrt_Lbc
===> done in files util_lbc.c util_lbc.h and exc_lbc.c

9) Replace the 0,1 of the enum by their respective definition: Cod, Dec,
Both...
===> done in file lbccodec.c

10) For some compilers, a pointer problem was found in the 5.3 codebook
searching procedure. It must be corrected in G.723 and G.729.
===> procedure D4i64_LBC() is updated in file exc_lbc.c

11) Correct some comments (spell errors)

12) Modifications introduced to avoid instabilities in case of
mistracking between the encoder and the decoder :

12.1) Sine wave detection :
Modification of lpc.c
Insertion of SinDet in structure CodStat (in file cst_lbc.h).

12.2) Taming procedure :
- Insertion of the two functions Update_Err and Test_Err in exc_lbc.c
(modification of exc_lbc.c & exc_lbc.h) :
Update_Err makes an estimation of the potential error introduced on
the excitation at the decoder in case of mistracking.
Test_Err evaluates the maximum excitation error for a given delay range
and outputs an index used to constraint the choice of the long term gain
vector.
- Modification of Find_Acbk() in exc_lbc.c : the index value given by
Test_Err is used to compute the bounds for the search in the tables
AcbkGainTable085 and AcbkGainTable170
- Modifications of tab_lbc.c (and tab_lbc.h) :
The vectors of AcbkGainTable085, AcbkGainTable170 epsi170 and
gain170 have been reordered.
The table AcbkGainBound[] has been suppressed (replaced by the 2 constants
NbFilt085 and NbFilt170 in cst_lbc.h)
The tables tabgain85 and tabgain170 have been added, providing an
associated 1-tap gain for each gain vector (in increasing order).
- Modification of cst_lbc.h to introduce new constants used for the taming
procedure, and introduction of the array Err[] in structure CodStat.

13) At the decoder, introduction of a procedure forcing Crc = 1 in case
of forbidden codes detection (modification of Decod() in decod.c and
Line_Unpk() in util_lbc.c)

14) Explicit initialization of the static structures CodStat and DecStat :
function Init_Coder() in coder.c and Init_Decod() in decod.c.

15) Various cosmetic changes regarding file handling in lbccodec.c and
util_lbc.c (Line_Rd(), Line_Wr()).

16) Insertion of __unix in typedef.h

17) In Line_Unpk() (file util_lbc.c) : check if the decoded bitrate
corresponds to the selected one. If not, exit with an error message.