代数码书搜索（固定码书搜索）
经过自适应码本搜索后，语音信号的时域相关性被极大地去除了，剩下的残差信号接近于随机信号。 残差信号是与一个伪随机的固定码本进行"匹配"，算出最佳的码本索引与增益。
// ---
/*-----------------------------------------------------*
* - Innovative codebook search. *
*-----------------------------------------------------*/
index = ACELP_Codebook(xn2, h1, T0, sharp, i_subfr, code, y2, &i);
*ana++ = index; /* Positions index */
*ana++ = i; /* Signs index */
固定码书搜索
固定码本搜索与g723的固定码本搜索算法几乎是一模一样的。g729与g723另一个不同的是，增益的估值与量化，这些笔者将在后继的章节分析。
ACELP_Codebook和g723的ACELP_LBC_code函数算法是一模一样的。
Word16 ACELP_Codebook( /* (o) :index of pulses positions */ // 激励信号索引
Word16 x[], /* (i) :Target vector */ // 目标向量
Word16 h[], /* (i) Q12 :Impulse response of filters */ // 滤波器冲击响应
Word16 T0, /* (i) :Pitch lag */ // 基音延迟
Word16 pitch_sharp, /* (i) Q14 :Last quantized pitch gain */ // 上一次量化的基音增益
Word16 i_subfr, /* (i) :Indicator of 1st subframe, */ // 是否是第一个子帧
Word16 code[], /* (o) Q13 :Innovative codebook */ // 新的码书
Word16 y[], /* (o) Q12 :Filtered innovative codebook */ // 滤波后的新码书
Word16 *sign /* (o) :Signs of 4 pulses */ // 冲击的符号
)
//--
// 如果基音延迟T小于子帧长度，则将固定增益基音贡献算入冲击响应，并计算自相关
/*-----------------------------------------------------------------*
* Include fixed-gain pitch contribution into impulse resp. h[] *
* Find correlations of h[] needed for the codebook search. *
*-----------------------------------------------------------------*/
sharp = shl(pitch_sharp, 1); /* From Q14 to Q15 */
if (sub(T0, L_SUBFR)<0) // 前置预滤波
for (i = T0; i < L_SUBFR; i++){ /* h[i] += pitch_sharp*h[i-T0] */
h[i] = add(h[i], mult(h[i-T0], sharp));
}
Cor_h(h, rr); // 计算自相关
// 计算目标矢量和冲击响应的互相关
/*-----------------------------------------------------------------*
* Compute correlation of target vector with impulse response. *
*-----------------------------------------------------------------*/
Cor_h_X(h, x, Dn);
// 查找码书
/*-----------------------------------------------------------------*
* Find innovative codebook. *
*-----------------------------------------------------------------*/
index = D4i40_17(Dn, rr, h, code, y, sign, i_subfr);
// 将固定增益基音贡献算入码矢量
/*-----------------------------------------------------------------*
* Compute innovation vector gain. *
* Include fixed-gain pitch contribution into code[]. *
*-----------------------------------------------------------------*/
if(sub(T0 ,L_SUBFR) <0)
for (i = T0; i < L_SUBFR; i++) { /* code[i] += pitch_sharp*code[i-T0] */
code[i] = add(code[i], mult(code[i-T0], sharp));
}
return index; // 返回码书索引值
代数码书搜索
需要计算的公式如下：
H=\begin{bmatrix}
h(0) & 0 & 0 & ... & 0 \\
h(1) & h(0) & 0 & ... & 0 \\
h(2) & h(1) & h(0) & ... & 0 \\
... & ... & ... & ... & ... \\
h(39)& h(38)& h(37) & ... & h(0)
\end{bmatrix}
H^T=\begin{bmatrix}
h(0) & h(1) & h(2) & ... & h(39) \\
0 & h(0) & h(1) & ... & h(38) \\
0 & 0 & h(0) & ... & h(37) \\
... & ... & ... & ... & ... \\
0 & 0 & 0 & ... & h(0)
\end{bmatrix}
x=\begin{bmatrix}x(39) & x(38) & x(37) & ... & x(0)\end{bmatrix}
d=xH^T
d(i)=\sum_{n=i}^{39}x\prime(n)h(n-i)
C=|d(m_0)|+|d(m_1)|+|d(m_2)|+|d(m_3)|
\phi=H^TH
\phi\prime(i,j)=\frac{1}{2}*sign[d(i)]*sign[d(j)]*\phi(i,j)=\frac{1}{2}*sign[d(i)]*sign[d(j)]*\sum_{n=j}^{39}h(n-i)h(n-j)
\frac{E}{2}=\phi\prime(m_0, m_0)
+\phi\prime(m_1, m_1)+\phi\prime(m_0, m_1)
+\phi\prime(m_2, m_2)+\phi\prime(m_0, m_2)+\phi\prime(m_1, m_2)
+\phi\prime(m_3, m_3)+\phi\prime(m_0, m_3)+\phi\prime(m_1, m_3)+\phi\prime(m_2, m_3)
static Word16 D4i40_17( /* (o) : Index of pulses positions. */ // 冲击索引
Word16 Dn[], /* (i) : Correlations between h[] and Xn[]. */ // 冲击响应和目标矢量户相关
Word16 rr[], /* (i) : Correlations of impulse response h[]. */ // 冲击响应自相关
Word16 h[], /* (i) Q12: Impulse response of filters. */ // 滤波器冲击响应
Word16 cod[], /* (o) Q13: Selected algebraic codeword. */ // 选定的代数码书码字
Word16 y[], /* (o) Q12: Filtered algebraic codeword. */ // 滤波后代数码书码字
Word16 *sign, /* (o) : Signs of 4 pulses. */ // 冲击的符号
Word16 i_subfr /* (i) : subframe flag */ // 子帧标志
)
计算目标矢量和滤波器的互相关$d(i)$
// acelp_co.c -> Cor_h_X()
for (i = 0; i < L_SUBFR; i++)
{
s = 0;
for (j = i; j < L_SUBFR; j++)
s = L_mac(s, X[j], h[j-i]); // x(i)h(0)+x(i+1)h(1)+...
y32[i] = s; // 互相关值
s = L_abs(s);
L_temp =L_sub(s,max);
if(L_temp>0L) {
max = s; // 得到max，做归一化使用
}
}
计算目标矢量的自相关和互相关
| 名称 | 符号 | 位置 |
|---|---|---|
| m0 | (+-1) | 0, 5, 10, 15, 20, 25, 30, 35 |
| m1 | (+-1) | 1, 6, 11, 16, 21, 26, 31, 36 |
| m2 | (+-1) | 2, 7, 12, 17, 22, 27, 32, 37 |
| m3 | (+-1) | 3, 8, 13, 18, 23, 28, 33, 38 |
| m4 | (+-1) | 4, 9, 14, 19, 24, 29, 34, 39 |
在[JBoss - org.mobicents.media.server.impl.dsp.audio.g729.LD8KConstants]中的对应部分有如下注释
public static final short DIM_RR = 616; /* size of correlation matrix */
public static final short NB_POS = 8 ; /* Number of positions for each pulse */
public static final short STEP = 5 ; /* Step betweem position of the same pulse. */
public static final short MSIZE = 64 ; /* Size of vectors for cross-correlation between 2 pulses*/
从注释可已看出，NB_POS表示每个冲击可能的位置个数；STEP表示对于某个冲击，相邻位置的间隔；MSIZE表示两个冲击互相关可能取值的个数。
- 自相关
$R_{ii}$个数 = 3 NB_POS + (2NBPOS) = 3 8 + (216) = 40
`$|\phi{xx_11}$`$\phi_{xx\_22}$$\phi_{xx\_33}$$\phi_{xx\_44}$$\phi_{xx\_55}$$\phi_{xx\_66}$$\phi_{xx\_77}$$\phi_{xx\_88}|$ 互相关
$R_{ij}$个数 = 3 64 + 3 (816) = 192 + 3 128 = 576
$|\phi_{xy\_11}$$\phi_{xy\_12}$$\phi_{xy\_13}$$\phi_{xy\_14}$$\phi_{xy\_15}$$\phi_{xy\_16}$$\phi_{xy\_17}$$\phi_{xy\_18}|$$|\phi_{yx\_12}$$\phi_{xy\_22}$$\phi_{xy\_23}$$\phi_{xy\_24}$$\phi_{xy\_25}$$\phi_{xy\_26}$$\phi_{xy\_27}$$\phi_{xy\_28}|$$|\phi_{yx\_13}$$\phi_{yx\_23}$$\phi_{xy\_33}$$\phi_{xy\_34}$$\phi_{xy\_35}$$\phi_{xy\_36}$$\phi_{xy\_37}$$\phi_{xy\_38}|$$|\phi_{yx\_14}$$\phi_{yx\_24}$$\phi_{yx\_34}$$\phi_{xy\_44}$$\phi_{xy\_45}$$\phi_{xy\_46}$$\phi_{xy\_47}$$\phi_{xy\_48}|$$|\phi_{yx\_15}$$\phi_{yx\_25}$$\phi_{yx\_35}$$\phi_{yx\_45}$$\phi_{xy\_55}$$\phi_{xy\_56}$$\phi_{xy\_57}$$\phi_{xy\_58}|$$|\phi_{yx\_16}$$\phi_{yx\_26}$$\phi_{yx\_36}$$\phi_{yx\_46}$$\phi_{yx\_56}$$\phi_{xy\_66}$$\phi_{xy\_67}$$\phi_{xy\_68}|$$|\phi_{yx\_17}$$\phi_{yx\_27}$$\phi_{yx\_37}$$\phi_{yx\_47}$$\phi_{yx\_57}$$\phi_{yx\_67}$$\phi_{xy\_77}$$\phi_{xy\_78}|$$|\phi_{yx\_18}$$\phi_{yx\_28}$$\phi_{yx\_38}$$\phi_{yx\_48}$$\phi_{yx\_58}$$\phi_{yx\_68}$$\phi_{yx\_78}$$\phi_{xy\_88}|$- 总个数 = 自相关个数 + 互相关个数 = 616
代码当中处理时，位置3的16个可能取值被分为两组进行处理，而且计算时不计算这两组间的互相关，结果是一样的。
首先计算自相关，示例如下
\phi(i,i)=\sum_{n=i}^{39}h(n-i)h(n-i)
\phi(39,39)=h(0)h(0)
\phi(38,38)=h(0)h(0)+h(1)h(1)
\phi(37,37)=h(0)h(0)+h(1)h(1)+h(2)h(2)
...
代码如下：
/*
* i0 (+-1) : 0, 5, 10, 15, 20, 25, 30, 35 *
* i1 (+-1) : 1, 6, 11, 16, 21, 26, 31, 36 *
* i2 (+-1) : 2, 7, 12, 17, 22, 27, 32, 37 *
* i3 (+-1) : 3, 8, 13, 18, 23, 28, 33, 38 *
* 4, 9, 14, 19, 24, 29, 34, 39 *
*/
ptr_h1 = h;
cor = 0;
for(i=0; i<NB_POS; i++)
{
// fai_hihi, i=0,1,2,3,4....
cor = L_mac(cor, *ptr_h1, *ptr_h1); ptr_h1++; // 0, 5, 10, 15, 20, 25, 30, 35
*p4-- = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h1); ptr_h1++;
*p3-- = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h1); ptr_h1++;
*p2-- = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h1); ptr_h1++;
*p1-- = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h1); ptr_h1++;
*p0-- = extract_h(cor);
}
计算互相关时，由$\phi(i,j)$的计算公式
$\phi(i,j)=\sum_{n=j}^{39}h(n-i)h(n-j)$ $i=0,1,...,39$,$j=i,i+1,...,39$ 可知，
计算$m_0$和$m_1$的互相关性时，由于对索引的大小有要求，因此不是二者所有的组合都存在相关结果。
$m_0$和$m_1$存在两种关系：
- 关系1：
$m_0[i]<m_1[i]<m_1[i+1]<...<m_1[8]$，$R_{01}$对应图中红色位置。 - 关系2：
$m_0[8]>...>m_0[i+1]>m_1[i]$，$R_{10}$对应图中绿色位置。
其他任意两行的互相关都存在类似关系。
以$R_{01}$、$R_{12}$、$R_{23}$关系1和$R_{04}$关系2为例：
R_{01\_88}=\phi(37,38)=\sum_{n=38}^{39}h(n-37)h(n-38)=h(1)h(0)+h(2)h(1)
R_{12\_88}\phi(36,37)=\sum_{n=37}^{39}h(n-36)h(n-37)=h(1)h(0)+h(2)h(1)+h(3)h(2)
R_{23\_88}\phi(35,36)=\sum_{n=36}^{39}h(n-35)h(n-36)=h(1)h(0)+h(2)h(1)+h(3)h(2)+h(4)h(3)
R_{40\_78}\phi(34,35)=\sum_{n=35}^{39}h(n-34)h(n-35)=h(1)h(0)+h(2)h(1)+h(3)h(2)+h(4)h(3)+h(5)h(4)
...
对应代码如下：
/*
* i4 (+-1) : 4, 9, 14, 19, 24, 29, 34, 39 *
* i0 (+-1) : 0, 5, 10, 15, 20, 25, 30, 35 *
* i1 (+-1) : 1, 6, 11, 16, 21, 26, 31, 36 *
* i2 (+-1) : 2, 7, 12, 17, 22, 27, 32, 37 *
* i3 (+-1) : 3, 8, 13, 18, 23, 28, 33, 38 *
*/
/*-----------------------------------------------------------------*
* Compute elements of: rri2i3[上], rri1i2[上], rri0i1[上] and rri0i4[下] *
*-----------------------------------------------------------------*/
l_fin_sup = MSIZE-1;
l_fin_inf = l_fin_sup-(Word16)1;
ldec = NB_POS+1;
ptr_hd = h;
ptr_hf = ptr_hd + 1;
for(k=0; k<NB_POS; k++) {
// ROUND 1
p3 = rri2i3 + l_fin_sup;
p2 = rri1i2 + l_fin_sup;
p1 = rri0i1 + l_fin_sup;
p0 = rri0i4 + l_fin_inf; // rri4i0
cor = 0;
ptr_h1 = ptr_hd;
ptr_h2 = ptr_hf;
for(i=k+(Word16)1; i<NB_POS; i++ ) {
// round 1
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // h0*h1
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_37_38=h0*h1+h1*h2
*p3 = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_36_37=h0*h1+h1*h2+h2*h3
*p2 = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_35_36=h0*h1+h1*h2+h2*h3+h3*h4
*p1 = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_34_35=h0*h1+h1*h2+h2*h3+h3*h4+h4*h5
*p0 = extract_h(cor);
p3 -= ldec; // -=9
p2 -= ldec;
p1 -= ldec;
p0 -= ldec;
// round 2
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // h5*h6
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_32_33=h0*h1+h1*h2+h2*h3+h3*h4+h4*h5+h6*h7+
*p3 = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_31_32=h0*h1+h1*h2+h2*h3+h3*h4+h4*h5+h6*h7+h7*h8+
*p2 = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_30_31=h0*h1+h1*h2+h2*h3+h3*h4+h4*h5+h6*h7+h7*h8+h8*h9
*p1 = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_29_30=h0*h1+h1*h2+h2*h3+h3*h4+h4*h5+h6*h7+h7*h8+h8*h9+h9*h10
*p0 = extract_h(cor);
p3 -= ldec; // -=9
p2 -= ldec;
p1 -= ldec;
p0 -= ldec;
// round 3
...
}
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++;
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_2_3
*p3 = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_1_2
*p2 = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_0_1
*p1 = extract_h(cor);
l_fin_sup -= NB_POS;
l_fin_inf--;
ptr_hf += STEP;
// ROUND 2
p3 = rri2i3 + l_fin_sup;
p2 = rri1i2 + l_fin_sup;
p1 = rri0i1 + l_fin_sup;
p0 = rri0i4 + l_fin_inf; // rri4i0
cor = 0;
ptr_h1 = ptr_hd;
ptr_h2 = ptr_hf;
for(i=k+(Word16)1; i<NB_POS; i++ ) {
// round 1
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // h0*h6
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_32_38=h0*h6+h1*h7
*p3 = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_31_37=h0*h6+h1*h7+h2*h8
*p2 = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_30_36=h0*h6+h1*h7+h2*h8+h3*h9
*p1 = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_29_35=h0*h6+h1*h7+h2*h8+h3*h9+h4*h10
*p0 = extract_h(cor);
p3 -= ldec; // -=9
p2 -= ldec;
p1 -= ldec;
p0 -= ldec;
// round 2
...
}
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++;
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_2_8
*p3 = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_1_7
*p2 = extract_h(cor);
cor = L_mac(cor, *ptr_h1, *ptr_h2); ptr_h1++; ptr_h2++; // R_0_6
*p1 = extract_h(cor);
l_fin_sup -= NB_POS;
l_fin_inf--;
ptr_hf += STEP;
// ROUND 3
...
}
实际搜索
- 得到互相关值的符号
- 通过前3个冲击和滤波器的互相关，得到搜索门限
- 搜索找出最大的三个值的和
$max_3$ - 搜索找出三个值和的平均值
$avg_3$ - 计算门限
$thr_3=avg_3+k*(max_3-avg_3)$，$k=0.4$
- 搜索找出最大的三个值的和
- 计算互相关
$\phi$，将冲击的符号考虑进去（只考虑互相关部分即可）
通过最大化$\frac{correlation^2}{energy}$的值，搜索4个冲击所在的最佳位置。实现时，搜索是通过4层嵌套实现的。每层嵌套当中，一个冲击会分别影响自相关和能量。
只有当前3个冲击得到的自相关超过预设门限时，才会进入第4个循环。
ps_0=d[i_0]
ps_1=ps_0+d[i_1]=d[i_0]+d[i_1]
ps_2=ps_1+d[i_2]=d[i_0]+d[i_1]+d[i_2]
ps_3=ps_2+d[i_3]=d[i_0]+d[i_1]+d[i_2]+d[i_3]
ps_3\_c=ps_3*ps_3
\alpha_0=R_{0\_0}[i]
\alpha_1=\alpha_0 + R_{1\_1}[i] + 2 * R_{0\_1}[i]
\alpha_2=\alpha_1 + R_{2\_2}[i] + 2 * \left(R_{0\_2}[i]+R_{1\_2}[i]\right)
\alpha_3=\alpha_2 + R_{3\_3}[i] + 2 * \left(R_{0\_3}[i]+R_{1\_3}[i]+R_{2\_3}[i]\right)
把求商的最值，变换成乘积差的比较，得到最大值对应的冲击位置。
ps_3*ps_3*\alpha - psc*\alpha_3 > 0
==>>
\frac{ps_3*ps_3}{alpha_3}>\frac{psc}{\alpha}
// --
time = add(MAX_TIME, extra); // 首帧搜索(75+30=105)次，其他帧等于(75+上次搜索剩余次数)。
for (i0 = 0; i0 < L_SUBFR; i0 += STEP) /* first pulse loop */
{
ps0 = Dn[i0];
alp0 = *ptr_ri0i0++;
ptr_ri1i1 = rri1i1; /* Init. pointers that depend on second loop */
ptr_ri1i2 = rri1i2;
ptr_ri1i3 = rri1i3;
ptr_ri1i4 = rri1i4;
for (i1 = 1; i1 < L_SUBFR; i1 += STEP) /* second pulse loop */
{
ps1 = add(ps0, Dn[i1]); // Dn[i0]+Dn[i1]
/* alp1 = alp0 + *ptr_ri1i1++ + 2.0 * ( *ptr_ri0i1++); */
alp1 = L_mult(alp0, 1);
alp1 = L_mac(alp1, *ptr_ri1i1++, 1);
alp1 = L_mac(alp1, *ptr_ri0i1++, 2);
ptr_ri2i2 = rri2i2; /* Init. pointers that depend on third loop */
ptr_ri2i3 = rri2i3;
ptr_ri2i4 = rri2i4;
for (i2 = 2; i2 < L_SUBFR; i2 += STEP) /* third pulse loop */
{
ps2 = add(ps1, Dn[i2]);
/* alp2 = alp1 + *ptr_ri2i2++ + 2.0 * (*ptr_ri0i2++ + *ptr_ri1i2++); */
alp2 = L_mac(alp1, *ptr_ri2i2++, 1);
alp2 = L_mac(alp2, *ptr_ri0i2++, 2);
alp2 = L_mac(alp2, *ptr_ri1i2++, 2);
/* Test threshold */
if ( sub(ps2, thres) > 0)
{
ptr_ri3i3 = rri3i3; /* Init. pointers that depend on 4th loop */
for (i3 = 3; i3 < L_SUBFR; i3 += STEP) /* 4th pulse loop */
{
ps3 = add(ps2, Dn[i3]);
/* alp3 = alp2 + *ptr_ri3i3++ */
/* + 2.0*( *ptr_ri0i3++ + *ptr_ri1i3++ + *ptr_ri2i3++); */
alp3 = L_mac(alp2, *ptr_ri3i3++, 1);
alp3 = L_mac(alp3, *ptr_ri0i3++, 2);
alp3 = L_mac(alp3, *ptr_ri1i3++, 2);
alp3 = L_mac(alp3, *ptr_ri2i3++, 2);
alp = extract_l(L_shr(alp3, 5));
ps3c = mult(ps3, ps3); // L_temp = ps3*ps3*alpha - psc*alp
L_temp = L_mult(ps3c, alpha);
L_temp = L_msu(L_temp, psc, alp);
if( L_temp > 0L )
{
psc = ps3c;
alpha = alp;
ip0 = i0;
ip1 = i1;
ip2 = i2;
ip3 = i3;
}
} /* end of for i3 = */
ptr_ri0i3 -= NB_POS;
ptr_ri1i3 -= NB_POS;
ptr_ri4i4 = rri4i4; /* Init. pointers that depend on 4th loop */
for (i3 = 4; i3 < L_SUBFR; i3 += STEP) /* 4th pulse loop */
{
ps3 = add(ps2, Dn[i3]);
/* alp3 = alp2 + *ptr_ri4i4++ */
/* + 2.0*( *ptr_ri0i4++ + *ptr_ri1i4++ + *ptr_ri2i4++); */
alp3 = L_mac(alp2, *ptr_ri4i4++, 1);
alp3 = L_mac(alp3, *ptr_ri0i4++, 2);
alp3 = L_mac(alp3, *ptr_ri1i4++, 2);
alp3 = L_mac(alp3, *ptr_ri2i4++, 2);
alp = extract_l(L_shr(alp3, 5));
ps3c = mult(ps3, ps3);
L_temp = L_mult(ps3c, alpha);
L_temp = L_msu(L_temp, psc, alp);
if( L_temp > 0L )
{
psc = ps3c;
alpha = alp;
ip0 = i0;
ip1 = i1;
ip2 = i2;
ip3 = i3;
}
} /* end of for i3 = */
ptr_ri0i4 -= NB_POS;
ptr_ri1i4 -= NB_POS;
time = sub(time, 1);
if(time <= 0 ) goto end_search; // 限定搜索次数，超出后退出 /* Maximum time finish */
} /* end of if >thres */
else
{
ptr_ri2i3 += NB_POS;
ptr_ri2i4 += NB_POS;
}
} /* end of for i2 = */
ptr_ri0i2 -= NB_POS;
ptr_ri1i3 += NB_POS;
ptr_ri1i4 += NB_POS;
} /* end of for i1 = */
ptr_ri0i2 += NB_POS;
ptr_ri0i3 += NB_POS;
ptr_ri0i4 += NB_POS;
} /* end of for i0 = */
y[i]=\sum_{i=0}^{n}{cod[i]h[n-i]}=\sum_{k=1}^{4}{cod[i_k]h[n-i_k]}
i3 (+-1):
3, 8, 13, 18, 23, 28, 33, 38
4, 9, 14, 19, 24, 29, 34, 39
上下两行除以5得到的结果相同，因而必须额外增加一个信息表示是哪一行的位置。
end_search:
extra = time; // 下次额外搜索次数，等于本次剩余次数（循环正常结束时））
/* Set the sign of impulses */
i0 = p_sign[ip0]; // 得到对应冲击的符号
i1 = p_sign[ip1];
i2 = p_sign[ip2];
i3 = p_sign[ip3];
/* Find the codeword corresponding to the selected positions */
for(i=0; i<L_SUBFR; i++) {cod[i] = 0; } // 得到搜索结果对应的码字
cod[ip0] = shr(i0, 2); /* From Q15 to Q13 */
cod[ip1] = shr(i1, 2);
cod[ip2] = shr(i2, 2);
cod[ip3] = shr(i3, 2);
/* find the filtered codeword */
// 只需计算非0位置的冲击即可。
for (i = 0; i < L_SUBFR; i++) {y[i] = 0; }
if(i0 > 0)
for(i=ip0, j=0; i<L_SUBFR; i++, j++) {
y[i] = add(y[i], h[j]); }
else
for(i=ip0, j=0; i<L_SUBFR; i++, j++) {
y[i] = sub(y[i], h[j]); }
if(i1 > 0)
for(i=ip1, j=0; i<L_SUBFR; i++, j++) {
y[i] = add(y[i], h[j]); }
else
for(i=ip1, j=0; i<L_SUBFR; i++, j++) {
y[i] = sub(y[i], h[j]); }
if(i2 > 0)
for(i=ip2, j=0; i<L_SUBFR; i++, j++) {
y[i] = add(y[i], h[j]); }
else
for(i=ip2, j=0; i<L_SUBFR; i++, j++) {
y[i] = sub(y[i], h[j]); }
if(i3 > 0)
for(i=ip3, j=0; i<L_SUBFR; i++, j++) {
y[i] = add(y[i], h[j]); }
else
for(i=ip3, j=0; i<L_SUBFR; i++, j++) {
y[i] = sub(y[i], h[j]); }
/* find codebook index; 17-bit address */
// 保存符号位
i = 0;
if(i0 > 0) i = add(i, 1);
if(i1 > 0) i = add(i, 2);
if(i2 > 0) i = add(i, 4);
if(i3 > 0) i = add(i, 8);
*sign = i;
// 保存码字对应位置索引
ip0 = mult(ip0, 6554); /* ip0/5 */
ip1 = mult(ip1, 6554); /* ip1/5 */
ip2 = mult(ip2, 6554); /* ip2/5 */
i = mult(ip3, 6554); /* ip3/5 */
j = add(i, shl(i, 2)); /* j = i*5 */
j = sub(ip3, add(j, 3)); /* j= ip3%5 -3 */
ip3 = add(shl(i, 1), j); // 行信息，保存在ip3的最后一个bit位
// 保存到一个Word16当中
i = add(ip0, shl(ip1, 3));
i = add(i , shl(ip2, 6));
i = add(i , shl(ip3, 9));
return i; // 保存着冲击位置的信息
计算固定码字的增益，计算时考虑自适应码书的结果。
如果基音延迟$T_0<40$，则将$[T_0,40)$之间的的值重新用以下公式计算。
code[i] = code[i]+pitch_sharp*cod[i-T_0],i=[T_0,40)
/*-----------------------------------------------------------------*
* Compute innovation vector gain. *
* Include fixed-gain pitch contribution into code[]. *
*-----------------------------------------------------------------*/
if(sub(T0 ,L_SUBFR) <0)
for (i = T0; i < L_SUBFR; i++) { /* code[i] += pitch_sharp*code[i-T0] */
code[i] = add(code[i], mult(code[i-T0], sharp));
}