dec_lpc.c
上传用户:dangjiwu
上传日期:2013-07-19
资源大小:42019k
文件大小:20k
- /*
- *===================================================================
- * 3GPP AMR Wideband Floating-point Speech Codec
- *===================================================================
- */
- #include "typedef.h"
- #include "dec_util.h"
- #define M 16 /* Order of LP filter */
- #define MP1 (M + 1)
- #define M16k 20
- #define NC16k (M16k / 2)
- #define MU 10923 /* Prediction factor (1.0/3.0) in Q15 */
- #define L_MEANBUF 3
- #define ALPHA 29491 /* 0. 9 in Q15 */
- #define ONE_ALPHA (32768-ALPHA) /* (1.0 - ALPHA) in Q15 */
- #define ORDER 16 /* order of linear prediction filter */
- #define ISF_GAP 128 /* 50 Hz */
- #define INV_LENGTH 2731 /* 1/12 */
- extern const Word16 D_ROM_dico1_isf[];
- extern const Word16 D_ROM_dico2_isf[];
- extern const Word16 D_ROM_dico21_isf_36b[];
- extern const Word16 D_ROM_dico22_isf_36b[];
- extern const Word16 D_ROM_dico23_isf_36b[];
- extern const Word16 D_ROM_dico21_isf[];
- extern const Word16 D_ROM_dico22_isf[];
- extern const Word16 D_ROM_dico23_isf[];
- extern const Word16 D_ROM_dico24_isf[];
- extern const Word16 D_ROM_dico25_isf[];
- extern const Word16 D_ROM_dico1_isf_noise[];
- extern const Word16 D_ROM_dico2_isf_noise[];
- extern const Word16 D_ROM_dico3_isf_noise[];
- extern const Word16 D_ROM_dico4_isf_noise[];
- extern const Word16 D_ROM_dico5_isf_noise[];
- extern const Word16 D_ROM_mean_isf[];
- extern const Word16 D_ROM_mean_isf_noise[];
- extern const Word16 D_ROM_cos[];
- /*
- * D_LPC_isf_reorder
- *
- * Parameters:
- * isf I/O: vector of isfs
- * min_dist I: quantized ISFs (in frequency domain)
- * n I: LPC order
- *
- * Function:
- * To make sure that the isfs are properly order and to keep a certain
- * minimum distance between consecutive isfs.
- *
- * Returns:
- * void
- */
- static void D_LPC_isf_reorder(Word16 *isf, Word16 min_dist, Word16 n)
- {
- Word32 i, isf_min;
- isf_min = min_dist;
- for(i = 0; i < n - 1; i++)
- {
- if(isf[i] < isf_min)
- {
- isf[i] = (Word16)isf_min;
- }
- isf_min = isf[i] + min_dist;
- }
- return;
- }
- /*
- * D_LPC_isf_noise_d
- *
- * Parameters:
- * indice I: indices of the selected codebook entries
- * isf_q O: quantized ISFs (in frequency domain)
- *
- * Function:
- * Decoding of ISF parameters
- *
- * Returns:
- * void
- */
- void D_LPC_isf_noise_d(Word16 *indice, Word16 *isf_q)
- {
- Word32 i;
- for(i = 0; i < 2; i++)
- {
- isf_q[i] = D_ROM_dico1_isf_noise[indice[0] * 2 + i];
- }
- for(i = 0; i < 3; i++)
- {
- isf_q[i + 2] = D_ROM_dico2_isf_noise[indice[1] * 3 + i];
- }
- for(i = 0; i < 3; i++)
- {
- isf_q[i + 5] = D_ROM_dico3_isf_noise[indice[2] * 3 + i];
- }
- for(i = 0; i < 4; i++)
- {
- isf_q[i + 8] = D_ROM_dico4_isf_noise[indice[3] * 4 + i];
- }
- for(i = 0; i < 4; i++)
- {
- isf_q[i + 12] = D_ROM_dico5_isf_noise[indice[4] * 4 + i];
- }
- for(i = 0; i < ORDER; i++)
- {
- isf_q[i] = (Word16)(isf_q[i]+ D_ROM_mean_isf_noise[i]);
- }
- D_LPC_isf_reorder(isf_q, ISF_GAP, ORDER);
- return;
- }
- /*
- * D_LPC_isf_isp_conversion
- *
- * Parameters:
- * isp O: (Q15) isp[m] (range: -1<=val<1)
- * isf I: (Q15) isf[m] normalized (range: 0.0 <= val <= 0.5)
- * m I: LPC order
- *
- * Function:
- * Transformation isf to isp
- *
- * ISP are immitance spectral pair in cosine domain (-1 to 1).
- * ISF are immitance spectral pair in frequency domain (0 to 6400).
- * Returns:
- * void
- */
- void D_LPC_isf_isp_conversion(Word16 isf[], Word16 isp[], Word16 m)
- {
- Word32 i, ind, offset, tmp;
- for(i = 0; i < m - 1; i++)
- {
- isp[i] = isf[i];
- }
- isp[m - 1] = (Word16)(isf[m - 1] << 1);
- for(i = 0; i < m; i++)
- {
- ind = isp[i] >> 7; /* ind = b7-b15 of isf[i] */
- offset = isp[i] & 0x007f; /* offset = b0-b6 of isf[i] */
- /* isp[i] = table[ind]+ ((table[ind+1]-table[ind])*offset) / 128 */
- tmp = (D_ROM_cos[ind + 1] - D_ROM_cos[ind]) * offset;
- isp[i] = (Word16)(D_ROM_cos[ind] + (tmp >> 7));
- }
- return;
- }
- /*
- * D_LPC_isp_pol_get
- *
- * Parameters:
- * isp I: Immitance spectral pairs (cosine domaine)
- * f O: the coefficients of F1 or F2
- * n I: no of coefficients (m/2)
- * k16 I: 16k flag
- *
- * Function:
- * Find the polynomial F1(z) or F2(z) from the ISPs.
- * This is performed by expanding the product polynomials:
- *
- * F1(z) = product ( 1 - 2 isp_i z^-1 + z^-2 )
- * i=0,2,4,6,8
- * F2(z) = product ( 1 - 2 isp_i z^-1 + z^-2 )
- * i=1,3,5,7
- *
- * where isp_i are the ISPs in the cosine domain.
- *
- * Returns:
- * void
- */
- static void D_LPC_isp_pol_get(Word16 *isp, Word32 *f, Word32 n, Word16 k16)
- {
- Word32 i, j, t0, s1, s2;
- Word16 hi, lo;
- s1 = 8388608;
- s2 = 512;
- if(k16)
- {
- s1 >>= 2;
- s2 >>= 2;
- }
- /* All computation in Q23 */
- f[0] = s1; /* f[0] = 1.0; in Q23 */
- f[1] = isp[0] * (-s2); /* f[1] = -2.0*isp[0] in Q23 */
- f += 2; /* Advance f pointer */
- isp += 2; /* Advance isp pointer */
- for(i = 2; i <= n; i++)
- {
- *f = f[ - 2];
- for(j = 1; j < i; j++, f--)
- {
- D_UTIL_l_extract(f[- 1], &hi, &lo);
- t0 = D_UTIL_mpy_32_16(hi, lo, *isp); /* t0 = f[-1] * isp */
- t0 = (t0 << 1);
- *f = (*f - t0); /* *f -= t0 */
- *f = (*f + f[ - 2]); /* *f += f[-2] */
- }
- *f = *f - (*isp * s2); /* *f -= isp << 8 */
- f += i; /* Advance f pointer */
- isp += 2; /* Advance isp pointer */
- }
- return;
- }
- /*
- * D_LPC_isp_a_conversion
- *
- * Parameters:
- * isp I: (Q15) Immittance spectral pairs
- * a O: (Q12) Predictor coefficients (order = M)
- * m I: order of LP filter
- *
- * Function:
- * Convert ISPs to predictor coefficients a[]
- *
- * Returns:
- * void
- */
- void D_LPC_isp_a_conversion(Word16 isp[], Word16 a[], Word16 m)
- {
- Word32 j, i, nc;
- Word32 f1[NC16k + 1], f2[NC16k];
- Word32 t0;
- Word16 hi, lo;
- nc = m >> 1;
- if(nc > 8)
- {
- D_LPC_isp_pol_get(&isp[0], f1, nc, 1);
- for(i = 0; i <= nc; i++)
- {
- f1[i] = (f1[i] << 2);
- }
- }
- else
- {
- D_LPC_isp_pol_get(&isp[0], f1, nc, 0);
- }
- if(nc > 8)
- {
- D_LPC_isp_pol_get(&isp[1], f2, nc - 1, 1);
- for(i = 0; i <= nc - 1; i++)
- {
- f2[i] = (f2[i] << 2);
- }
- }
- else
- {
- D_LPC_isp_pol_get(&isp[1], f2, nc - 1, 0);
- }
- /*
- * Multiply F2(z) by (1 - z^-2)
- */
- for(i = nc - 1; i > 1; i--)
- {
- f2[i] = f2[i] - f2[i - 2]; /* f2[i] -= f2[i-2]; */
- }
- /*
- * Scale F1(z) by (1+isp[m-1]) and F2(z) by (1-isp[m-1])
- */
- for(i = 0; i < nc; i++)
- {
- /* f1[i] *= (1.0 + isp[M-1]); */
- D_UTIL_l_extract(f1[i], &hi, &lo);
- t0 = D_UTIL_mpy_32_16(hi, lo, isp[m - 1]);
- f1[i] = f1[i] + t0;
- /* f2[i] *= (1.0 - isp[M-1]); */
- D_UTIL_l_extract(f2[i], &hi, &lo);
- t0 = D_UTIL_mpy_32_16(hi, lo, isp[m - 1]);
- f2[i] = f2[i] - t0;
- }
- /*
- * A(z) = (F1(z)+F2(z))/2
- * F1(z) is symmetric and F2(z) is antisymmetric
- */
- /* a[0] = 1.0; */
- a[0] = 4096;
- for(i = 1, j = m - 1; i < nc; i++, j--)
- {
- /* a[i] = 0.5*(f1[i] + f2[i]); */
- t0 = f1[i] + f2[i]; /* f1[i] + f2[i] */
- a[i] = (Word16)((t0 + 0x800) >> 12); /* from Q23 to Q12 and * 0.5 */
- /* a[j] = 0.5*(f1[i] - f2[i]); */
- t0 = (f1[i] - f2[i]); /* f1[i] - f2[i] */
- a[j] = (Word16)((t0 + 0x800) >> 12); /* from Q23 to Q12 and * 0.5 */
- }
- /* a[NC] = 0.5*f1[NC]*(1.0 + isp[M-1]); */
- D_UTIL_l_extract(f1[nc], &hi, &lo);
- t0 = D_UTIL_mpy_32_16(hi, lo, isp[m - 1]);
- t0 = (f1[nc] + t0);
- a[nc] = (Word16)((t0 + 0x800) >> 12); /* from Q23 to Q12 and * 0.5 */
- /* a[m] = isp[m-1]; */
- a[m] = (Word16)((isp[m - 1] + 0x4) >> 3); /* from Q15 to Q12 */
- return;
- }
- /*
- * D_LPC_a_weight
- *
- * Parameters:
- * a I: LP filter coefficients
- * ap O: weighted LP filter coefficients
- * gamma I: weighting factor
- * m I: order of LP filter
- *
- * Function:
- * Weighting of LP filter coefficients, ap[i] = a[i] * (gamma^i).
- *
- * Returns:
- * void
- */
- void D_LPC_a_weight(Word16 a[], Word16 ap[], Word16 gamma, Word16 m)
- {
- Word32 i, fac;
- ap[0] = a[0];
- fac = gamma;
- for(i = 1; i < m; i++)
- {
- ap[i] = (Word16)(((a[i] * fac) + 0x4000) >> 15);
- fac = ((fac * gamma) + 0x4000) >> 15;
- }
- ap[m] = (Word16)(((a[m] * fac) + 0x4000) >> 15);
- return;
- }
- /*
- * D_LPC_isf_2s3s_decode
- *
- * Parameters:
- * indice I: quantisation indices
- * isf_q O: quantised ISFs in the cosine domain
- * past_isfq I/O: past ISF quantizer
- * isfold I: past quantised ISF
- * isf_buf O: isf buffer
- * bfi I: Bad frame indicator
- *
- * Function:
- * Decoding of ISF parameters.
- *
- * Returns:
- * void
- */
- void D_LPC_isf_2s3s_decode(Word16 *indice, Word16 *isf_q, Word16 *past_isfq,
- Word16 *isfold, Word16 *isf_buf, Word16 bfi)
- {
- Word32 ref_isf[M];
- Word32 L_tmp, i, j;
- Word16 tmp;
- if(bfi == 0) /* Good frame */
- {
- for(i = 0; i < 9; i++)
- {
- isf_q[i] = D_ROM_dico1_isf[indice[0] * 9 + i];
- }
- for(i = 0; i < 7; i++)
- {
- isf_q[i + 9] = D_ROM_dico2_isf[indice[1] * 7 + i];
- }
- for(i = 0; i < 5; i++)
- {
- isf_q[i] =
- (Word16)(isf_q[i] + D_ROM_dico21_isf_36b[indice[2] * 5 + i]);
- }
- for(i = 0; i < 4; i++)
- {
- isf_q[i + 5] =
- (Word16)(isf_q[i + 5] + D_ROM_dico22_isf_36b[indice[3] * 4 + i]);
- }
- for(i = 0; i < 7; i++)
- {
- isf_q[i + 9] =
- (Word16)(isf_q[i + 9] + D_ROM_dico23_isf_36b[indice[4] * 7 + i]);
- }
- for(i = 0; i < ORDER; i++)
- {
- tmp = isf_q[i];
- isf_q[i] =
- (Word16)((tmp + D_ROM_mean_isf[i]) + ((MU * past_isfq[i]) >> 15));
- past_isfq[i] = tmp;
- }
- for(i = 0; i < M; i++)
- {
- for(j = (L_MEANBUF - 1); j > 0; j--)
- {
- isf_buf[j * M + i] = isf_buf[(j - 1) * M + i];
- }
- isf_buf[i] = isf_q[i];
- }
- }
- else
- { /* bad frame */
- for(i = 0; i < M; i++)
- {
- L_tmp = D_ROM_mean_isf[i];
- for(j = 0; j < L_MEANBUF; j++)
- {
- L_tmp = L_tmp + isf_buf[j * M + i];
- }
- ref_isf[i] = (L_tmp + 0x1) >> 2;
- }
- /* use the past ISFs slightly shifted towards their mean */
- for(i = 0; i < ORDER; i++)
- {
- isf_q[i] = (Word16)((((ALPHA * isfold[i]) >> 15) +
- ((ONE_ALPHA * ref_isf[i]) >> 15)));
- }
- /* estimate past quantized residual to be used in next frame */
- for(i = 0; i < ORDER; i++)
- {
- /* predicted ISF */
- L_tmp = ref_isf[i] + ((past_isfq[i] * MU) >> 15);
- /* past_isfq[i] *= 0.5 */
- past_isfq[i] = (Word16)((isf_q[i] - L_tmp) >> 1);
- }
- }
- D_LPC_isf_reorder(isf_q, ISF_GAP, ORDER);
- return;
- }
- /*
- * D_LPC_isf_2s5s_decode
- *
- * Parameters:
- * indice I: quantization indices
- * isf_q O: quantized ISFs in the cosine domain
- * past_isfq I/O: past ISF quantizer
- * isfold I: past quantized ISF
- * isf_buf O: isf buffer
- * bfi I: Bad frame indicator
- *
- * Function:
- * Decoding of ISF parameters.
- *
- * Returns:
- * void
- */
- void D_LPC_isf_2s5s_decode(Word16 *indice, Word16 *isf_q, Word16 *past_isfq,
- Word16 *isfold, Word16 *isf_buf, Word16 bfi)
- {
- Word32 ref_isf[M];
- Word32 i, j, L_tmp;
- Word16 tmp;
- if(bfi == 0) /* Good frame */
- {
- for(i = 0; i < 9; i++)
- {
- isf_q[i] = D_ROM_dico1_isf[indice[0] * 9 + i];
- }
- for(i = 0; i < 7; i++)
- {
- isf_q[i + 9] = D_ROM_dico2_isf[indice[1] * 7 + i];
- }
- for(i = 0; i < 3; i++)
- {
- isf_q[i] = (Word16)(isf_q[i] + D_ROM_dico21_isf[indice[2] * 3 + i]);
- }
- for(i = 0; i < 3; i++)
- {
- isf_q[i + 3] =
- (Word16)(isf_q[i + 3] + D_ROM_dico22_isf[indice[3] * 3 + i]);
- }
- for(i = 0; i < 3; i++)
- {
- isf_q[i + 6] =
- (Word16)(isf_q[i + 6] + D_ROM_dico23_isf[indice[4] * 3 + i]);
- }
- for(i = 0; i < 3; i++)
- {
- isf_q[i + 9] =
- (Word16)(isf_q[i + 9] + D_ROM_dico24_isf[indice[5] * 3 + i]);
- }
- for(i = 0; i < 4; i++)
- {
- isf_q[i + 12] =
- (Word16)(isf_q[i + 12] + D_ROM_dico25_isf[indice[6] * 4 + i]);
- }
- for(i = 0; i < ORDER; i++)
- {
- tmp = isf_q[i];
- isf_q[i] =
- (Word16)((tmp + D_ROM_mean_isf[i]) + ((MU * past_isfq[i]) >> 15));
- past_isfq[i] = tmp;
- }
- for(i = 0; i < M; i++)
- {
- for(j = (L_MEANBUF - 1); j > 0; j--)
- {
- isf_buf[j * M + i] = isf_buf[(j - 1) * M + i];
- }
- isf_buf[i] = isf_q[i];
- }
- }
- else
- { /* bad frame */
- for(i = 0; i < M; i++)
- {
- L_tmp = D_ROM_mean_isf[i];
- for(j = 0; j < L_MEANBUF; j++)
- {
- L_tmp = L_tmp + isf_buf[j * M + i];
- }
- ref_isf[i] = (L_tmp + 0x1) >> 2;
- }
- /* use the past ISFs slightly shifted towards their mean */
- for(i = 0; i < ORDER; i++)
- {
- isf_q[i] = (Word16)(((ALPHA * isfold[i]) >> 15) +
- ((ONE_ALPHA * ref_isf[i]) >> 15));
- }
- /* estimate past quantized residual to be used in next frame */
- for(i = 0; i < ORDER; i++)
- {
- /* predicted ISF */
- L_tmp = ref_isf[i] + ((past_isfq[i] * MU) >> 15);
- /* past_isfq[i] *= 0.5 */
- past_isfq[i] = (Word16)((isf_q[i] - L_tmp) >> 1);
- }
- }
- D_LPC_isf_reorder(isf_q, ISF_GAP, ORDER);
- return;
- }
- /*
- * D_LPC_int_isp_find
- *
- * Parameters:
- * isp_old I: isps from past frame
- * isp_new I: isps from present frame
- * frac I: (Q15) fraction for 3 first subfr
- * Az O: LP coefficients in 4 subframes
- *
- * Function:
- * Find the interpolated ISP parameters for all subframes.
- *
- * Returns:
- * void
- */
- void D_LPC_int_isp_find(Word16 isp_old[], Word16 isp_new[],
- const Word16 frac[], Word16 Az[])
- {
- Word32 tmp, i, k, fac_old, fac_new;
- Word16 isp[M];
- for(k = 0; k < 3; k++)
- {
- fac_new = frac[k];
- fac_old = (32767 - fac_new) + 1; /* 1.0 - fac_new */
- for(i = 0; i < M; i++)
- {
- tmp = isp_old[i] * fac_old;
- tmp += isp_new[i] * fac_new;
- isp[i] = (Word16)((tmp + 0x4000) >> 15);
- }
- D_LPC_isp_a_conversion(isp, Az, M);
- Az += MP1;
- }
- /* 4th subframe: isp_new (frac=1.0) */
- D_LPC_isp_a_conversion(isp_new, Az, M);
- return;
- }
- /*
- * D_LPC_isf_extrapolation
- *
- * Parameters:
- * HfIsf I/O: ISF vector
- *
- * Function:
- * Conversion of 16th-order 12.8kHz ISF vector
- * into 20th-order 16kHz ISF vector
- *
- * Returns:
- * void
- */
- void D_LPC_isf_extrapolation(Word16 HfIsf[])
- {
- Word32 IsfDiff[M - 2];
- Word32 IsfCorr[3];
- Word32 tmp, tmp2, tmp3, mean, i;
- Word32 MaxCorr, exp, exp2, coeff;
- Word16 hi, lo;
- HfIsf[M16k - 1] = HfIsf[M - 1];
- /* Difference vector */
- for(i = 1; i < M - 1; i++)
- {
- IsfDiff[i - 1] = HfIsf[i] - HfIsf[i - 1];
- }
- tmp = 0;
- /* Mean of difference vector */
- for(i = 3; i < (M - 1); i++)
- {
- tmp = tmp + (IsfDiff[i - 1] * INV_LENGTH);
- }
- mean = (tmp + 0x4000) >> 15;
- IsfCorr[0] = 0;
- IsfCorr[1] = 0;
- IsfCorr[2] = 0;
- tmp = 0;
- for(i = 0; i < M - 2; i++)
- {
- if(IsfDiff[i] > tmp)
- {
- tmp = IsfDiff[i];
- }
- }
- exp = D_UTIL_norm_s((Word16)tmp);
- for(i = 0; i < M - 2; i++)
- {
- IsfDiff[i] = IsfDiff[i] << exp;
- }
- mean = mean << exp;
- for(i = 7; i < M - 2; i++)
- {
- tmp2 = IsfDiff[i] - mean;
- tmp3 = IsfDiff[i - 2] - mean;
- tmp = (tmp2 * tmp3) << 1;
- D_UTIL_l_extract(tmp, &hi, &lo);
- tmp = D_UTIL_mpy_32(hi, lo, hi, lo);
- IsfCorr[0] = (IsfCorr[0] + tmp);
- }
- for(i = 7; i < M - 2; i++)
- {
- tmp2 = IsfDiff[i] - mean;
- tmp3 = IsfDiff[i - 3] - mean;
- tmp = (tmp2 * tmp3) << 1;
- D_UTIL_l_extract(tmp, &hi, &lo);
- tmp = D_UTIL_mpy_32(hi, lo, hi, lo);
- IsfCorr[1] = (IsfCorr[1] + tmp);
- }
- for(i = 7; i < M - 2; i++)
- {
- tmp2 = IsfDiff[i] - mean;
- tmp3 = IsfDiff[i - 4] - mean;
- tmp = (tmp2 * tmp3) << 1;
- D_UTIL_l_extract(tmp, &hi, &lo);
- tmp = D_UTIL_mpy_32(hi, lo, hi, lo);
- IsfCorr[2] = (IsfCorr[2] + tmp);
- }
- if(IsfCorr[0] > IsfCorr[1])
- {
- MaxCorr = 0;
- }
- else
- {
- MaxCorr = 1;
- }
- if(IsfCorr[2] > IsfCorr[MaxCorr])
- {
- MaxCorr = 2;
- }
- MaxCorr = MaxCorr + 1; /* Maximum correlation of difference vector */
- for(i = M - 1; i < (M16k - 1); i++)
- {
- tmp = (HfIsf[i - 1 - MaxCorr] - HfIsf[i - 2 - MaxCorr]);
- HfIsf[i] = (Word16)(HfIsf[i - 1] + tmp);
- }
- /* tmp=7965+(HfIsf[2]-HfIsf[3]-HfIsf[4])/6; */
- tmp = HfIsf[4] + HfIsf[3];
- tmp = HfIsf[2] - tmp;
- tmp = (tmp * 5461) >> 15;
- tmp = tmp + 20390;
- if(tmp > 19456)
- { /* Maximum value of ISF should be at most 7600 Hz */
- tmp = 19456;
- }
- tmp = tmp - HfIsf[M - 2];
- tmp2 = HfIsf[M16k - 2] - HfIsf[M - 2];
- exp2 = D_UTIL_norm_s((Word16)tmp2);
- exp = D_UTIL_norm_s((Word16)tmp);
- exp = exp - 1;
- tmp = tmp << exp;
- tmp2 = tmp2 << exp2;
- coeff = (tmp << 15) / tmp2; /* Coefficient for stretching the ISF vector */
- exp = exp2 - exp;
- if(exp >= 0)
- {
- for(i = M - 1; i < M16k - 1; i++)
- {
- tmp = ((HfIsf[i] - HfIsf[i - 1]) * coeff) >> 15;
- IsfDiff[i - (M - 1)] = tmp << exp;
- }
- }
- else
- {
- exp = 15 - exp;
- for(i = M - 1; i < M16k - 1; i++)
- {
- IsfDiff[i - (M - 1)] = ((HfIsf[i] - HfIsf[i - 1]) * coeff) >> exp;
- }
- }
- for(i = M; i < (M16k - 1); i++)
- {
- /* The difference between ISF(n) and ISF(n-2) should be at least 500 Hz */
- tmp = ((IsfDiff[i - (M - 1)] + IsfDiff[i - M]) - 1280);
- if(tmp < 0)
- {
- if(IsfDiff[i - (M - 1)] > IsfDiff[i - M])
- {
- IsfDiff[i - M] = (1280 - IsfDiff[i - (M - 1)]);
- }
- else
- {
- IsfDiff[i - (M - 1)] = (1280 - IsfDiff[i - M]);
- }
- }
- }
- for(i = M - 1; i < M16k - 1; i++)
- {
- HfIsf[i] = (Word16)(HfIsf[i - 1] + IsfDiff[i - (M - 1)]);
- }
- for(i = 0; i < M16k - 1; i++)
- {
- HfIsf[i] = (Word16)((HfIsf[i] * 13107) >> 14);
- /* Scale the ISF vector correctly for 16000 kHz */
- }
- D_LPC_isf_isp_conversion(HfIsf, HfIsf, M16k);
- return;
- }