?? lpcfunc.c
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/* Version 3.3 Last modified: December 26, 1995 */
/*-------------------------------------------------------------*
* Procedure Lsp_Az: *
* ~~~~~~ *
* Compute the LPC coefficients from lsp (order=10) *
*-------------------------------------------------------------*/
#include "typedef.h"
#include "basic_op.h"
#include "oper_32b.h"
#include "ld8k.h"
#include "tab_ld8k.h"
/* local function */
static void Get_lsp_pol(Word16 *lsp, Word32 *f);
void Lsp_Az(
Word16 lsp[], /* (i) Q15 : line spectral frequencies */
Word16 a[] /* (o) Q12 : predictor coefficients (order = 10) */
)
{
Word16 i, j;
Word32 f1[6], f2[6];
Word32 t0;
Get_lsp_pol(&lsp[0],f1);
Get_lsp_pol(&lsp[1],f2);
for (i = 5; i > 0; i--)
{
f1[i] = L_add(f1[i], f1[i-1]); /* f1[i] += f1[i-1]; */
f2[i] = L_sub(f2[i], f2[i-1]); /* f2[i] -= f2[i-1]; */
}
a[0] = 4096;
for (i = 1, j = 10; i <= 5; i++, j--)
{
t0 = L_add(f1[i], f2[i]); /* f1[i] + f2[i] */
a[i] = extract_l( L_shr_r(t0, 13) ); /* from Q24 to Q12 and * 0.5 */
t0 = L_sub(f1[i], f2[i]); /* f1[i] - f2[i] */
a[j] = extract_l( L_shr_r(t0, 13) ); /* from Q24 to Q12 and * 0.5 */
}
return;
}
/*-----------------------------------------------------------*
* procedure Get_lsp_pol: *
* ~~~~~~~~~~~ *
* Find the polynomial F1(z) or F2(z) from the LSPs *
*-----------------------------------------------------------*
* *
* Parameters: *
* lsp[] : line spectral freq. (cosine domain) in Q15 *
* f[] : the coefficients of F1 or F2 in Q24 *
*-----------------------------------------------------------*/
static void Get_lsp_pol(Word16 *lsp, Word32 *f)
{
Word16 i,j, hi, lo;
Word32 t0;
/* All computation in Q24 */
*f = L_mult(4096, 2048); /* f[0] = 1.0; in Q24 */
f++;
*f = L_msu((Word32)0, *lsp, 512); /* f[1] = -2.0 * lsp[0]; in Q24 */
f++;
lsp += 2; /* Advance lsp pointer */
for(i=2; i<=5; i++)
{
*f = f[-2];
for(j=1; j<i; j++, f--)
{
L_Extract(f[-1] ,&hi, &lo);
t0 = Mpy_32_16(hi, lo, *lsp); /* t0 = f[-1] * lsp */
t0 = L_shl(t0, 1);
*f = L_add(*f, f[-2]); /* *f += f[-2] */
*f = L_sub(*f, t0); /* *f -= t0 */
}
*f = L_msu(*f, *lsp, 512); /* *f -= lsp<<9 */
f += i; /* Advance f pointer */
lsp += 2; /* Advance lsp pointer */
}
return;
}
/*___________________________________________________________________________
| |
| Functions : Lsp_lsf and Lsf_lsp |
| |
| Lsp_lsf Transformation lsp to lsf |
| Lsf_lsp Transformation lsf to lsp |
|---------------------------------------------------------------------------|
| Algorithm: |
| |
| The transformation from lsp[i] to lsf[i] and lsf[i] to lsp[i] are |
| approximated by a look-up table and interpolation. |
|___________________________________________________________________________|
*/
void Lsf_lsp(
Word16 lsf[], /* (i) Q15 : lsf[m] normalized (range: 0.0<=val<=0.5) */
Word16 lsp[], /* (o) Q15 : lsp[m] (range: -1<=val<1) */
Word16 m /* (i) : LPC order */
)
{
Word16 i, ind, offset;
Word32 L_tmp;
for(i=0; i<m; i++)
{
ind = shr(lsf[i], 8); /* ind = b8-b15 of lsf[i] */
offset = lsf[i] & (Word16)0x00ff; /* offset = b0-b7 of lsf[i] */
/* lsp[i] = table[ind]+ ((table[ind+1]-table[ind])*offset) / 256 */
L_tmp = L_mult(sub(table[ind+1], table[ind]), offset);
lsp[i] = add(table[ind], extract_l(L_shr(L_tmp, 9)));
}
return;
}
void Lsp_lsf(
Word16 lsp[], /* (i) Q15 : lsp[m] (range: -1<=val<1) */
Word16 lsf[], /* (o) Q15 : lsf[m] normalized (range: 0.0<=val<=0.5) */
Word16 m /* (i) : LPC order */
)
{
Word16 i, ind, tmp;
Word32 L_tmp;
ind = 63; /* begin at end of table -1 */
for(i= m-(Word16)1; i >= 0; i--)
{
/* find value in table that is just greater than lsp[i] */
while( sub(table[ind], lsp[i]) < 0 )
{
ind = sub(ind,1);
}
/* acos(lsp[i])= ind*256 + ( ( lsp[i]-table[ind] ) * slope[ind] )/4096 */
L_tmp = L_mult( sub(lsp[i], table[ind]) , slope[ind] );
tmp = round(L_shl(L_tmp, 3)); /*(lsp[i]-table[ind])*slope[ind])>>12*/
lsf[i] = add(tmp, shl(ind, 8));
}
return;
}
/*___________________________________________________________________________
| |
| Functions : Lsp_lsf and Lsf_lsp |
| |
| Lsp_lsf Transformation lsp to lsf |
| Lsf_lsp Transformation lsf to lsp |
|---------------------------------------------------------------------------|
| Algorithm: |
| |
| The transformation from lsp[i] to lsf[i] and lsf[i] to lsp[i] are |
| approximated by a look-up table and interpolation. |
|___________________________________________________________________________|
*/
void Lsf_lsp2(
Word16 lsf[], /* (i) Q13 : lsf[m] (range: 0.0<=val<PI) */
Word16 lsp[], /* (o) Q15 : lsp[m] (range: -1<=val<1) */
Word16 m /* (i) : LPC order */
)
{
Word16 i, ind;
Word16 offset; /* in Q8 */
Word16 freq; /* normalized frequency in Q15 */
Word32 L_tmp;
for(i=0; i<m; i++)
{
/* freq = abs_s(freq);*/
freq = mult(lsf[i], 20861); /* 20861: 1.0/(2.0*PI) in Q17 */
ind = shr(freq, 8); /* ind = b8-b15 of freq */
offset = freq & (Word16)0x00ff; /* offset = b0-b7 of freq */
if ( sub(ind, 63)>0 ){
ind = 63; /* 0 <= ind <= 63 */
}
/* lsp[i] = table2[ind]+ (slope_cos[ind]*offset >> 12) */
L_tmp = L_mult(slope_cos[ind], offset); /* L_tmp in Q28 */
lsp[i] = add(table2[ind], extract_l(L_shr(L_tmp, 13)));
}
return;
}
void Lsp_lsf2(
Word16 lsp[], /* (i) Q15 : lsp[m] (range: -1<=val<1) */
Word16 lsf[], /* (o) Q13 : lsf[m] (range: 0.0<=val<PI) */
Word16 m /* (i) : LPC order */
)
{
Word16 i, ind;
Word16 offset; /* in Q15 */
Word16 freq; /* normalized frequency in Q16 */
Word32 L_tmp;
ind = 63; /* begin at end of table2 -1 */
for(i= m-(Word16)1; i >= 0; i--)
{
/* find value in table2 that is just greater than lsp[i] */
while( sub(table2[ind], lsp[i]) < 0 )
{
ind = sub(ind,1);
if ( ind <= 0 )
break;
}
offset = sub(lsp[i], table2[ind]);
/* acos(lsp[i])= ind*512 + (slope_acos[ind]*offset >> 11) */
L_tmp = L_mult( slope_acos[ind], offset ); /* L_tmp in Q28 */
freq = add(shl(ind, 9), extract_l(L_shr(L_tmp, 12)));
lsf[i] = mult(freq, 25736); /* 25736: 2.0*PI in Q12 */
}
return;
}
/*-------------------------------------------------------------*
* procedure Weight_Az *
* ~~~~~~~~~ *
* Weighting of LPC coefficients. *
* ap[i] = a[i] * (gamma ** i) *
* *
*-------------------------------------------------------------*/
void Weight_Az(
Word16 a[], /* (i) Q12 : a[m+1] LPC coefficients */
Word16 gamma, /* (i) Q15 : Spectral expansion factor. */
Word16 m, /* (i) : LPC order. */
Word16 ap[] /* (o) Q12 : Spectral expanded LPC coefficients */
)
{
Word16 i, fac;
ap[0] = a[0];
fac = gamma;
for(i=1; i<m; i++)
{
ap[i] = round( L_mult(a[i], fac) );
fac = round( L_mult(fac, gamma) );
}
ap[m] = round( L_mult(a[m], fac) );
return;
}
/*----------------------------------------------------------------------*
* Function Int_qlpc() and Int_lpc() *
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ *
* Interpolation of the LPC parameters. *
*----------------------------------------------------------------------*/
/* Interpolation of the quantized LSP's */
void Int_qlpc(
Word16 lsp_old[], /* input : LSP vector of past frame */
Word16 lsp_new[], /* input : LSP vector of present frame */
Word16 Az[] /* output: interpolated Az() for the 2 subframes */
)
{
Word16 i;
Word16 lsp[M];
/* lsp[i] = lsp_new[i] * 0.5 + lsp_old[i] * 0.5 */
for (i = 0; i < M; i++) {
lsp[i] = add(shr(lsp_new[i], 1), shr(lsp_old[i], 1));
}
Lsp_Az(lsp, Az); /* Subframe 1 */
Lsp_Az(lsp_new, &Az[MP1]); /* Subframe 2 */
return;
}
/*----------------------------------------------------------------------*
* Function Int_lpc() *
* ~~~~~~~~~~~~~~~~~~ *
* Interpolation of the unquantized LPC parameters. *
* Same as the previous function but we do not recompute Az() for *
* subframe 2 because it is already available. *
* We also compute the interpolate LSF (frequency domain). *
*----------------------------------------------------------------------*/
void Int_lpc(
Word16 lsp_old[], /* input : LSP vector of past frame */
Word16 lsp_new[], /* input : LSP vector of present frame */
Word16 lsf_int[], /* output: interpolated lsf coefficients */
Word16 lsf_new[],
Word16 Az[] /* output: interpolated Az() for the 2 subframes */
)
{
Word16 i;
Word16 lsp[M];
/* lsp[i] = lsp_new[i] * 0.5 + lsp_old[i] * 0.5 */
for (i = 0; i < M; i++) {
lsp[i] = add(shr(lsp_new[i], 1), shr(lsp_old[i], 1));
}
Lsp_Az(lsp, Az);
Lsp_lsf(lsp, lsf_int, M); /* transformation from LSP to LSF (freq.domain) */
Lsp_lsf(lsp_new, lsf_new, M); /* transformation from LSP to LSF (freq.domain) */
return;
}
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